Learn Hardcore Portuguese (Portugal): Eu guardo a fotografia na carteira.

emphasis: Eu guardo a fotografia na carteira. (I do, as opposed to someone else.)
contrast: Eu guardo, mas ele deita fora. (I keep it, but he throws it away.)

In a neutral sentence, Guardo a fotografia na carteira is perfectly natural.

What exactly does guardo mean here? Is it “I keep”, “I put”, or “I save”?

The verb guardar is quite flexible. In this sentence, it’s closest to “I keep” (as in “I keep the photo in my wallet”).

Common meanings of guardar:

to keep / store
- Guardo os documentos na gaveta. – I keep the documents in the drawer.
to put away / to put somewhere safe
- Guarda o dinheiro na carteira. – Put the money in (your) wallet.
to save (for later)
- Guardei um bocado de bolo para ti. – I saved a piece of cake for you.
to guard / watch over
- O polícia guarda o museu à noite. – The policeman guards the museum at night.

In this sentence, you’re saying that the usual place where the photograph is kept is in the wallet, not that you are right now in the act of putting it in.

Does guardo mean “I keep” or “I am keeping”? How does the present tense work in Portuguese?

Guardo is the present indicative (presente do indicativo). It can cover both:

habitual / general action – “I (usually) keep”
- Eu guardo a fotografia na carteira. – I keep the photograph in the wallet (that’s where it lives).
present time, right now (in some contexts) – similar to “I am keeping / I keep it now”
- Agora guardo a fotografia na carteira. – Now I’m keeping the photo in the wallet.

If you really want to emphasise an action happening right now, Portuguese also uses the progressive:

Estou a guardar a fotografia na carteira. – I am (right now) putting/keeping the photo in the wallet.

But in many cases where English uses “I am …‑ing”, Portuguese just uses the simple present: guardo.

Why is there an a before fotografia? Why not just guardo fotografia?

Here, a is the definite article “the”, not the preposition “to”.

a fotografia = the photograph
uma fotografia = a photograph
fotografia (with no article) is possible but sounds more generic or abstract and is less common for a specific item.

So:

Eu guardo a fotografia na carteira. – I keep the photograph in the wallet. (a specific one)
Eu guardo uma fotografia na carteira. – I keep a photograph in the wallet. (one, not specified)
Eu guardo fotografias na carteira. – I keep photographs in the wallet. (plural, in general)

Using the article in Portuguese is much more common than in English, even when English might omit it. Here, since you probably mean a specific photo, a fotografia is the natural choice.

Is a before fotografia a preposition (“to”) or an article (“the”)? How can I tell?

In a fotografia, a is the feminine singular definite article (“the”).

You can tell because:

It comes immediately before a noun that can take articles: a fotografia.
It doesn’t combine with another preposition (like em, de, para) here.
The meaning of the phrase matches “the photograph”, not “to photograph” or anything similar.

Compare:

a fotografia – the photograph (article)
à fotografia – to the photograph (preposition a
- article a, with grave accent; more common in writing/formal styles, especially in Pt‑BR; in Pt‑PT, much rarer and often avoided)

In your sentence there is no preposition a at all; just the article a.

Why is it na carteira and not em a carteira or something else?

Na is a contraction:

em + a → na (in + the → in the) for feminine nouns
em + o → no (in + the → in the) for masculine nouns

Since carteira is feminine:

em + a carteira → na carteira

So:

na carteira = in the wallet
no bolso = in the pocket (bolso is masculine)

You would almost never say em a carteira in normal speech; the contraction na is standard and required in correct written Portuguese too.

What does carteira mean in European Portuguese? Is it “wallet”, “purse”, or something else?

In European Portuguese, carteira most commonly means:

wallet (for money, cards, etc.)

Examples:

Onde está a minha carteira? – Where is my wallet?

It can also mean, depending on context:

ladies’ handbag – especially in expressions like carteira de senhora, though mala is more common for “handbag” in Pt‑PT.
school desk or student’s desk – Os alunos estão sentados nas carteiras.

In Eu guardo a fotografia na carteira, the most natural interpretation is wallet. Context would decide if it was a handbag instead.

Why is it carteira (feminine) and not masculine? How do I know the gender?

Portuguese nouns have grammatical gender. Carteira is feminine, which you can see from:

the article: a carteira (feminine “the”)
the ending ‑a, which often (not always) indicates feminine gender

There isn’t always a logical reason; you usually have to learn the gender with the noun:

a carteira – the wallet (feminine)
o bolso – the pocket (masculine)
a fotografia – the photograph (feminine)
o telefone – the phone (masculine)

A good habit: when you learn a new noun, learn it with its article:

a carteira
a fotografia

Can I say Eu guardo na carteira a fotografia, or does the object have to come before na carteira?

Standard word order is:

Subject – Verb – Object – Place
Eu guardo a fotografia na carteira.

Other orders are possible for emphasis or style, but they sound more marked:

Na carteira, eu guardo a fotografia. – In the wallet, I keep the photograph. (emphasis on “in the wallet”)
Eu guardo na carteira a fotografia. – grammatically possible, but less neutral; feels a bit stylised or poetic.

For everyday speech, keep:

Eu guardo a fotografia na carteira.

Could I say Eu guardo a fotografia na minha carteira to be more precise? Is the possessive normally omitted?

Yes, you can say:

Eu guardo a fotografia na *minha carteira. – I keep the photograph in *my wallet.

Both are correct:

na carteira – often understood as “in my wallet” if the context is clear and you’re talking about your own things.
na minha carteira – explicitly “in my wallet”, if you want to avoid any doubt.

In European Portuguese, it’s common to omit the possessive when context makes it obvious:

Lavei as mãos. – I washed my hands.
Vesti o casaco. – I put on my coat.

So na carteira is perfectly natural if it’s clearly your own wallet.

Can I use foto instead of fotografia? Are they different?

Yes, foto is a very common, shorter form of fotografia. In most everyday contexts, they mean the same thing.

Eu guardo a fotografia na carteira.
Eu guardo a foto na carteira.

Both are correct. Note that foto is still feminine:

a foto, uma foto, esta foto

This is because foto is an abbreviation of fotografia, which is feminine.

How do you pronounce Eu guardo a fotografia na carteira in European Portuguese?

Approximate European Portuguese pronunciation (not exact IPA, but close enough to guide you):

Eu – like “eh-oo” said quickly, almost [eɨw]
guardo – “GWAR-doo”
- g like in “go”
- stress on GUAR
a – short “uh” sound, very quick
fotografia – “fo-too-gra-FEE-uh”
- stress on fi: fo-tu-gra-FI-a
na – “nah” (short)
carteira – “kar-TAY-rah”
- stress on TEI / TAY

Spoken smoothly, it comes out something like:

“Eɨw GWAR-do a fo-tu-gra-FI-a na kar-TAY-ra.”

Remember that European Portuguese tends to reduce unstressed vowels (the small a’s and o’s become very short, like a schwa in English).