Když je v bytě ticho, moje babička spí dobře.

Když means when here. It introduces a subordinate clause: Když je v bytě ticho = When it is quiet in the apartment.

A Czech learner should notice that this first part sets the situation, and the main clause comes after it: moje babička spí dobře.

So the structure is:

Když... , ...

very much like English:

When... , ...

The comma separates the subordinate clause from the main clause.

• Když je v bytě ticho = subordinate clause
• moje babička spí dobře = main clause

In Czech, commas are used very regularly before or after subordinate clauses. Since the sentence starts with the Když clause, the comma comes before the main clause.

Je is the 3rd person singular form of být, meaning to be.

The phrase je ticho is a very common Czech way to say it is quiet or there is silence.

Czech often uses this kind of structure without an explicit subject like English it. So:

• Je ticho. = It is quiet.
• literally, it is something like is quiet/silence

English needs a subject like it, but Czech does not.

Because the preposition v meaning in requires the locative case when it expresses location.

The noun byt changes in the locative singular:

• nominative: byt
• locative: bytě

So:

• v bytě = in the apartment

This is a very important pattern in Czech: prepositions often require specific cases.

Because je ticho is a fixed, natural expression meaning it is quiet.

Here ticho is not describing a noun like an adjective would. You are not saying that some thing is quiet in the adjective sense, such as:

• tichý pokoj = a quiet room

Instead, you are describing the overall situation or atmosphere:

• Je ticho. = It is quiet.

So ticho is the normal word in this expression.

Moje babička is in the nominative case because it is the subject of the main clause.

In moje babička spí dobře:

• moje babička = the subject
• spí = the verb
• dobře = an adverb describing how she sleeps

So babička stays in the basic dictionary form here.

Yes, you could say just babička if the context already makes it clear whose grandmother you mean.

• Když je v bytě ticho, babička spí dobře.
• Když je v bytě ticho, moje babička spí dobře.

Both are possible.

Czech often omits possessives when they are obvious from context, sometimes more often than English does. But moje babička is completely correct and natural if you want to be explicit.

The infinitive is spát, meaning to sleep, but its present-tense forms change:

• spím = I sleep
• spíš = you sleep
• spí = he/she/it sleeps

So with moje babička = my grandmother / she, the correct form is spí.

This is just the normal present-tense conjugation of spát.

Because dobře is an adverb, and it describes the verb spí.

• spí dobře = sleeps well

If you used dobrá or dobrý, those would be adjective forms, which describe nouns, not verbs.

Compare:

• dobrá babička = a good grandmother
• babička spí dobře = grandmother sleeps well

So here the adverb dobře is exactly what you need.

Most naturally, it sounds like a general or repeated situation:

When it is quiet in the apartment, my grandmother sleeps well.

So it suggests a pattern or habit.

Czech present tense can describe:

• what is happening now
• what usually happens
• a general truth

Without extra context, this sentence is usually understood as a general statement.

Yes. Czech word order is more flexible than English word order.

For example, you could also say:

Moje babička spí dobře, když je v bytě ticho.

This means the same basic thing.

The version you were given starts with the Když clause, which puts focus on the condition or situation first. The other version starts with moje babička, which puts the person first.

So the difference is mostly about emphasis and flow, not basic meaning.

No, not exactly.

• byt = apartment / flat
• dům = house or building

So v bytě means in the apartment, not in the house.

If you changed the noun, you would also change the form for the correct case:

• v bytě = in the apartment
• v domě = in the house / building

Yes, you could, but the nuance is a little different.

• ticho = silence / quiet
• klid = calm / peace / quietness

So:

• je ticho emphasizes the lack of noise
• je klid emphasizes calmness or peacefulness more broadly

In this sentence, ticho is very natural if you mean that the apartment is not noisy, and because of that the grandmother sleeps well.