Learn Hardcore Portuguese (Portugal): Algumas pessoas vão ao mercado hoje. - Some people are going to the market today.

pessoa is feminine singular → alguma pessoa (some person / a certain person)
pessoas is feminine plural → algumas pessoas (some people)
algum = masculine singular
alguns = masculine plural

So:

algumas pessoas = some people (feminine plural → matches pessoas)
alguns rapazes = some boys (masculine plural → matches rapazes)

Using algum or alguns with pessoas would be a gender disagreement and sound wrong to a native speaker.

What nuance does algumas have? Is it “some”, “a few”, or “several”?

Algumas is a fairly neutral way to say some:

It usually suggests more than one, but not a very large number.
It’s similar to English some people or a few people; context decides how many you imagine.
It doesn’t have a strong “small number” feeling like only a few; it’s quite neutral.

You could contrast:

Poucas pessoas vão ao mercado hoje. – Few people are going to the market today. (emphasises small number)
Muitas pessoas vão ao mercado hoje. – Many people are going to the market today. (emphasises large number)
Algumas pessoas vão ao mercado hoje. – Some people are going to the market today. (neutral – just “some”)

Could I say umas pessoas instead of algumas pessoas?

You can say umas pessoas, but the nuance is slightly different:

algumas pessoas – neutral some people, often just informational.
umas pessoas – also means some people, but often sounds a bit more informal or vague, like “some people / these people (I’m vaguely referring to)”.

Examples of nuance:

Algumas pessoas vão ao mercado hoje. – Just stating a fact: some people are going.
Umas pessoas vão ao mercado hoje, outras ficam em casa. – Some people are going today, others are staying home. (slightly more conversational, looser grouping)

Both are grammatically correct; algumas pessoas is the more “neutral textbook” option here.

Why is it pessoas vão and not pessoas vai?

Portuguese verbs must agree with the number and person of the subject:

pessoa (one person) → vai (3rd person singular of ir)
- Uma pessoa vai ao mercado. – One person goes / is going to the market.
pessoas (more than one) → vão (3rd person plural)
- Algumas pessoas vão ao mercado. – Some people go / are going to the market.

The verb ir (to go) is irregular in the present tense:

eu vou
tu vais
ele / ela / você vai
nós vamos
vós ides (rare in modern speech)
eles / elas / vocês vão

Since algumas pessoas = they (3rd person plural), you must use vão.

What exactly does ao mean here?

Ao is a contraction of:

a (preposition: to)
o (definite article: the, masculine singular)

So:

a + o = ao

In this sentence:

vão a = (they) go to
o mercado = the market
vão ao mercado = (they) go to the market

Some related contractions:

a + a = à
- Vou à escola. – I go to (the) school.
a + os = aos
a + as = às

Mercado is masculine singular, so you get ao mercado.

Could I say vão para o mercado instead of vão ao mercado? Is there a difference?

Both are grammatically correct in European Portuguese, and often either is fine:

vão ao mercado – very natural here; common for going somewhere for a visit/errand.
vão para o mercado – also possible; para can emphasise the destination or purpose a bit more.

Subtle tendencies (not strict rules):

ir a / ir ao:
- Often used for going to places in a more neutral way.
- Common with routine activities:
  - Vou ao mercado. – I go to the market.
  - Vamos ao cinema. – We’re going to the cinema.
ir para / ir para o:
- Often used when you’re going to stay somewhere, or to stress the end destination:
  - Vou para casa. – I’m going home (to be there).
  - Ele vai para Lisboa. – He’s going to Lisbon (to live/work/spend time there).

In your sentence, Algumas pessoas vão ao mercado hoje is the most idiomatic choice; vão para o mercado is possible but not necessary.

Why is it ao mercado and not no mercado?

Because you’re talking about movement to a place, not location in a place.

ir a / ao = go to (movement)
estar em / no = be in / at (location)

Contractions:

a + o = ao → ir ao mercado = go to the market
em + o = no → estar no mercado = be in/at the market

So:

Algumas pessoas vão ao mercado hoje. – Some people are going to the market today.
Algumas pessoas estão no mercado hoje. – Some people are at/in the market today.

In European Portuguese, vão no mercado (go in the market) is not used for “go to the market”; it sounds wrong or very odd.

Why is the present tense vão used for something happening today? Shouldn’t it be future tense?

Portuguese often uses the simple present to talk about near future events, especially when there is a time expression like hoje (today), amanhã (tomorrow), logo (later):

Algumas pessoas vão ao mercado hoje.
= Some people are going to the market today.

This is similar to English using the present progressive for scheduled/near future:

“They are going to the market today.”

You could also express future in other ways:

Algumas pessoas irão ao mercado hoje. – They will go to the market today. (more formal / explicit future)
Algumas pessoas vão ir ao mercado hoje. – They are going to go to the market today. (grammatical but often feels clumsy; natives rarely say vão ir if vão alone is clear from context.)

In everyday European Portuguese, present + time expression is perfectly natural for near future.

Where can hoje go in the sentence? Are other word orders possible?

Yes, hoje is fairly flexible. All of these are grammatically correct:

Algumas pessoas vão ao mercado hoje.
Hoje, algumas pessoas vão ao mercado.
Algumas pessoas hoje vão ao mercado. (less common, but possible in speech for emphasis)

Nuances:

Hoje, algumas pessoas vão ao mercado.
- Emphasises today; it’s like starting with “Today, some people…”.
Algumas pessoas vão ao mercado hoje.
- Very neutral; probably the most natural version.

Placing hoje somewhere else usually just shifts the focus slightly; the basic meaning (“some people are going today”) stays the same.

What exactly does mercado mean here? Is it a supermarket, an open market, or something more general?

In European Portuguese:

mercado often suggests a physical market, especially a food market (with stalls, fresh produce, etc.).
supermercado is specifically supermarket.

So:

ir ao mercado – often understood as going to the town/city market (for fresh food).
ir ao supermercado – going to a supermarket (e.g., Continente, Pingo Doce).

However, in casual speech, depending on the town and habits, some people might use mercado a bit more loosely when they basically mean “the place where they buy food”. Context usually clarifies.

For abstract meanings like “the job market”, “the housing market”, mercado is also used, but there you’d have extra words:

o mercado de trabalho – the job market
o mercado imobiliário – the property market

Do we always need the article with mercado? Could we say vão a mercado?

With concrete places like mercado, Portuguese almost always uses a definite article:

vão ao mercado – correct
vão a mercado – wrong / unidiomatic in this everyday sense

Portuguese generally uses more definite articles with place nouns than English does:

Vou ao trabalho. – I’m going to (the) work.
Vou à escola. – I’m going to (the) school.

Some common exceptions where the article is often dropped (because the place is more like an idea of “home / school / church”):

Vou para casa. – I’m going home.
Vou à escola. vs Vou para a escola. (nuance, but article can appear or not depending on variety and context)
Vou à missa. – I’m going to (the) mass.

But with mercado in this everyday, literal sense, ao mercado is the natural form.

Is Algumas pessoas vão ao mercado hoje the only natural word order for the subject, or could I drop algumas or change it?

You have some flexibility, but the meaning changes:

Algumas pessoas vão ao mercado hoje.
- Some (but not all) people are going to the market today.
Pessoas vão ao mercado hoje.
- Grammatically possible, but unusual and feels incomplete or very “headline-like” in isolation.
- Could work in a context like a list of things that happen today:
  - Pessoas vão ao mercado hoje, turistas visitam o castelo, alunos fazem exame…
As pessoas vão ao mercado hoje.
- The people are going to the market today (a specific group everyone knows about) or “people (in general) are going to the market today” — depends on context.

Typically, you’d keep algumas here to make clear you mean some people and not all or people in general.

How do you pronounce Algumas pessoas vão ao mercado hoje in European Portuguese?

Very roughly, in an English-friendly approximation (European accent):

Algumas – “ahl-GOO-mash”
- al- like “al” in “album”
- -gu- like “goo”
- final -as often sounds like a soft “-ash” in European Portuguese
pessoas – “p’so-ahsh”
- the e is very reduced, almost like a quick “p-s”
- so like “so” in “sofa”
- final -as again like a soft “-ash”
vão – roughly “vown” (but nasal: let the sound resonate in your nose; don’t close with a clear n).
ao – “ow” (as in “cow”), but shorter.
mercado – “mehr-KAH-doo”
- mer like “mare” but shorter
- stress on -ca-: KAH
hoje – “OH-zh(ɨ)”
- ho- like “oh”
- -je is the soft French-like zh sound, plus a very weak final vowel.

Stringing it together (very approximate):

“ahl-GOO-mash p’so-ahsh VOWN ow mehr-KAH-doo OH-zh(ɨ)”

Native speech will be more connected and faster, but this gives you a starting point.