V mrazáku máme ještě jedno kuře, ale těstoviny musím koupit dnes.

Because v means in, and when it shows location, the noun after it usually goes into the locative case.

• base form: mrazák = freezer
• locative singular: v mrazáku = in the freezer

So this is a normal case change after v when you are saying where something is.

Here ještě means still or yet.

So máme ještě jedno kuře means:

• we still have one chicken
• or more naturally, we still have one chicken left

In other contexts, ještě can also mean more or another, so the phrase ještě jedno can sometimes feel like one more. In this sentence, the natural meaning is that there is still one chicken available in the freezer.

Because kuře is a neuter noun, and one has to agree with the noun’s gender.

The forms are:

• jeden = masculine
• jedna = feminine
• jedno = neuter

So:

• jedno kuře = one chicken

This is standard adjective/number agreement in Czech.

In this sentence, kuře most likely means a whole chicken for cooking/eating, not a live animal.

That is very natural in Czech. Compare:

• kuře = a chicken / a whole chicken
• kuřecí maso = chicken meat
• kuřecí = chicken, as an adjective

So V mrazáku máme ještě jedno kuře suggests there is one frozen chicken in the freezer.

Because Czech usually drops subject pronouns when they are not needed.

The verb endings already show who the subject is:

• máme = we have
• musím = I must / I have to

So Czech normally says:

• máme rather than my máme
• musím rather than já musím

You only add my or já if you want emphasis, contrast, or clarity.

Because the two clauses have different subjects, and that is completely normal.

• máme = we have
• musím koupit = I have to buy

So the meaning is something like:

• We still have one chicken in the freezer, but I have to buy pasta today.

This could mean that the chicken belongs to the household in general, but the speaker is the one responsible for buying the pasta.

Because in Czech, těstoviny is normally used as a plural noun meaning pasta.

That is just how the word behaves in everyday Czech, similar to how English often uses plural-type food words like noodles or spaghetti.

• těstoviny = pasta
• singular těstovina exists, but it usually means one pasta piece or is used in more technical contexts

So těstoviny musím koupit dnes is the normal way to say I have to buy pasta today.

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

• koupit = perfective → to buy, as a completed action
• kupovat = imperfective → to be buying / to buy repeatedly / to buy in general

In this sentence, musím koupit dnes means the speaker needs to complete the purchase today, so koupit is the natural choice.

If you used kupovat, it would sound more like focusing on the process, repetition, or a more general activity.

So:

• musím koupit těstoviny dnes = I need to buy pasta today
• musím kupovat těstoviny = I have to buy pasta regularly / I have to be buying pasta

Because Czech word order is fairly flexible, and the end of the sentence often carries important or new information.

So těstoviny musím koupit dnes puts a bit of focus on today.

Other word orders are also possible, for example:

• Dnes musím koupit těstoviny.
• Musím dnes koupit těstoviny.

All are grammatical, but the original version naturally highlights dnes at the end.

Because ale means but, and in Czech it normally introduces a new clause after a comma.

So this punctuation is standard:

• V mrazáku máme ještě jedno kuře, ale těstoviny musím koupit dnes.

In Czech writing, a comma before ale is expected in this kind of sentence.

Both are possible, but they sound slightly different because of emphasis and information structure.

• těstoviny musím koupit dnes
  This gives some emphasis to těstoviny, especially after the contrast with kuře.
• musím koupit těstoviny dnes
  This is also fine, but it sounds a little more neutral in some contexts.

The original sentence works well because it contrasts the two foods:

• we already have kuře
• but těstoviny are what need to be bought today

So the word order helps support that contrast.