Až budeme u moře, chci udělat fotku na pláži.

Here až means when / once, specifically referring to a future moment.

So:

• Až budeme u moře = When/Once we are at the seaside

A common beginner confusion is that až can also mean as late as / only, but not in this sentence. Here it introduces a future time clause.

That is a very common question. Czech works differently from English here.

After až, if you are talking about a future event, Czech normally uses a future form:

• Až budeme u moře... = When we are at the seaside...
• literally closer to When we will be...

So even though English avoids will after when, Czech does not have that restriction in the same way. Using budeme is completely normal.

Because Czech verbs usually show the subject by their endings.

• budeme = we will be
• chci = I want

So Czech often leaves out pronouns like my and já unless they are needed for emphasis or contrast.

You could say:

• Až my budeme u moře, já chci udělat fotku na pláži.

but that sounds unnecessarily emphatic in most situations.

U moře means by the sea / at the seaside.

That is different from:

• v moři = in the sea

So:

• Až budeme u moře means you are at the coast/seaside area
• it does not mean you are physically in the water

This is why u is used here.

The preposition u takes the genitive case.

So moře here is in the genitive singular.

A tricky part is that moře looks the same in nominative and genitive singular, so the form does not visibly change:

• nominative: moře
• genitive: moře

That is normal for some neuter nouns.

Because chci here expresses your current intention or wish about a future situation.

• Až budeme u moře, chci udělat fotku na pláži. = When we’re at the seaside, I want to take a photo on the beach.

This means: That is my plan / wish now.

If you said budu chtít, it would mean something more like:

• I will want to
• I expect that at that future time I’ll feel like it

That changes the meaning. In this sentence, chci is the natural choice.

This is about aspect, which is very important in Czech.

• udělat is perfective
• dělat is imperfective

Here, the speaker means one completed action: taking one photo. So Czech prefers the perfective verb:

• udělat fotku = to take a photo / make a photo as a completed act

Using dělat fotku would sound more like focusing on the process, repetition, or an unfinished action, and it is not the best choice here.

Yes, it is normal and common in everyday Czech.

Other common ways are:

• udělat fotku = everyday, natural
• vyfotit = to photograph / take a photo
• pořídit fotku/fotografii = a bit more formal or stylistically different

So this sentence could also be:

• Až budeme u moře, chci se vyfotit na pláži. if you mean I want to have a photo taken of myself
• Až budeme u moře, chci vyfotit pláž. if you mean I want to photograph the beach
• Až budeme u moře, chci udělat fotku na pláži. if you simply mean take a photo on the beach

Fotku is accusative singular of fotka.

• nominative: fotka
• accusative: fotku

It is in the accusative because it is the direct object of udělat:

• udělat co? → fotku

So literally: I want to make/take a photo.

Because na pláži expresses location, not movement.

• na pláži = on the beach / at the beach → locative
• na pláž = onto the beach / to the beach → accusative, motion toward a destination

In this sentence, the photo is being taken while on the beach, so Czech uses the locative:

• na pláži

It is the locative singular of pláž.

After na, when the meaning is location, Czech uses the locative:

• na pláži = on/at the beach

So this is a standard preposition + case pattern:

• na
  • locative = location
• na
  • accusative = direction/movement

Yes. Fotka is the everyday, informal word for photo.

A more neutral or formal word is:

• fotografie
• accusative singular: fotografii

So you could also say:

• Až budeme u moře, chci udělat fotografii na pláži.

That is correct, but it sounds a bit more formal or bookish. In normal conversation, fotku is very natural.

Yes. Czech word order is fairly flexible, although different orders can sound more natural depending on emphasis.

The original sentence is completely natural:

• Až budeme u moře, chci udělat fotku na pláži.

You could also hear:

• Až budeme u moře, chci na pláži udělat fotku.

Both are grammatical. The difference is mostly about emphasis and flow, not basic meaning.

By default, it usually describes where the photo is taken: on the beach.

So the most natural reading is:

• When we’re at the seaside, I want to take a photo on the beach.

Depending on context, listeners might also understand that the beach is part of the scene, but grammatically the phrase most naturally tells you the location of the action.