Moje sestra říká, že na této stanici je vždycky hodně lidí.

Both are possible.

• moje sestra = my sister
• má sestra = also my sister

The difference is mostly stylistic:

• moje is the full, more neutral form.
• má is a shorter form, often used in more literary or formal style, and sometimes for rhythm or emphasis.

In everyday speech, moje sestra is very common and natural.

Czech often leaves out subject pronouns when they are not needed.

In English, you must say My sister says... or She says...
In Czech, the subject is already clear from:

• the noun sestra
• the verb form říká = (she/he/it) says

So Moje sestra říká... is complete and natural without adding ona.

If you said Moje sestra, ta říká... or Ona říká..., that would add emphasis, but it is not necessary here.

říká is the 3rd person singular present tense of říkat, which means:

• to say
• to tell
• sometimes to be saying

So Moje sestra říká... means My sister says...

A useful contrast:

• říkat = imperfective, often for repeated or ongoing saying
• říct = perfective, usually to say as a completed act

Examples:

• Sestra říká, že... = My sister says that...
• Sestra řekla, že... = My sister said that...

že means that and introduces a subordinate clause.

So:

• Moje sestra říká = My sister says
• že na této stanici je vždycky hodně lidí = that there are always a lot of people at this station

Just like in English, that can sometimes be omitted:

• My sister says (that) ...

In Czech, že is usually kept and sounds very natural here.

With places like stations, platforms, stops, squares, and similar public locations, Czech often uses na where English uses at.

So:

• na stanici = at the station
• na zastávce = at the stop
• na náměstí = in/on the square, often best translated as in the square or at the square

Using v této stanici would usually sound wrong here.
For station as a location where people are present, Czech idiomatically says na stanici.

Because na here requires the locative case when it expresses location.

Base forms:

• tato = this
• stanice = station

Locative singular:

• na této stanici = at this station

So both words change to match the case:

• tato → této
• stanice → stanici

This is normal agreement: the demonstrative adjective must match the noun in gender, number, and case.

This is one of the most important patterns in Czech.

hodně means a lot of / many, and after quantity expressions like this, Czech usually uses:

• singular neuter verb: je
• noun in the genitive plural: lidí

So:

• je hodně lidí = literally something like there is a lot of people
• natural English: there are a lot of people

You will see the same pattern in many similar sentences:

• Je tu hodně aut. = There are a lot of cars here.
• Bylo tam málo času. = There was little time.
• Je ve městě mnoho turistů. = There are many tourists in the city.

So even though English uses are, Czech often uses singular je with expressions of quantity.

Because after hodně, the noun usually goes into the genitive plural.

The nominative plural of člověk / lidé is:

• lidé = people

But after hodně, you need the genitive plural:

• hodně lidí = a lot of people

So:

• lidé = subject form, nominative
• lidí = genitive plural form used after quantities

Compare:

• Lidé čekají. = People are waiting.
• Je tam hodně lidí. = There are a lot of people there.

Because the grammatical structure is centered on the quantity expression, not directly on people as a normal plural subject.

In Czech, expressions like:

• hodně lidí
• málo studentů
• spousta aut

often behave as a kind of quantity unit, and the verb is commonly singular:

• Je hodně lidí.
• Bylo tam málo studentů.
• Na ulici je spousta aut.

This is a normal Czech pattern, even though it feels strange to English speakers.

Both mean always.

• vždycky is very common in everyday speech.
• vždy is a bit shorter and can sound slightly more formal, literary, or concise depending on context.

In this sentence, vždycky sounds natural and conversational:

• je vždycky hodně lidí = there are always a lot of people

You could also say:

• je vždy hodně lidí

But vždycky is probably the more everyday choice.

Czech word order is flexible, but not random.
The sentence:

• na této stanici je vždycky hodně lidí

is a natural neutral order.

The adverb vždycky often goes near the verb or before the part it modifies. Here it modifies the whole idea that there are a lot of people, so its position after je sounds very natural.

Other word orders are possible, but they can shift emphasis:

• Na této stanici je vždycky hodně lidí. = neutral
• Na této stanici vždycky je hodně lidí. = stronger emphasis on always
• Vždycky je na této stanici hodně lidí. = also natural, with always highlighted earlier

So the original order is a standard, idiomatic way to say it.

Yes. stanice can mean several kinds of station, depending on context, for example:

• train station
• bus station
• metro station
• police station
• radio station
• TV station

In this sentence, because of na této stanici je vždycky hodně lidí, learners will usually understand it as a physical station where people gather, such as a train or metro station.

Context decides the exact meaning.

It is neutral, natural Czech.

Nothing in it is strongly formal or strongly slangy:

• Moje sestra = neutral
• říká, že = neutral
• na této stanici = neutral
• vždycky = everyday but completely standard
• hodně lidí = very common

So this is the kind of sentence you could hear in normal conversation and also write without any problem.

Yes.

• hodně lidí = many people
• hodně lidí = a lot of people

In normal English, a lot of people often sounds a bit more conversational, while many people can sound slightly more neutral or formal depending on context.

So the Czech phrase covers both very well.