Když mám teplotu, nejraději odpočívám doma a piji teplý čaj.

Here Když means when: When I have a fever...

It introduces a subordinate clause: Když mám teplotu.

In Czech, když can also sometimes be translated as if, depending on context, but in this sentence when is the most natural translation.

Because Když mám teplotu is a subordinate clause, and Czech normally separates subordinate clauses with a comma.

So the structure is:

• Když mám teplotu, = When I have a fever,
• nejraději odpočívám doma a piji teplý čaj. = main clause

This is very similar to English, where we also usually put a comma after an opening when-clause.

Yes, literally it does. But mít teplotu is a normal Czech expression meaning to have a fever or to be running a temperature.

So:

• mám teplotu = I have a fever / I’m running a temperature

This is one of those expressions that should be learned as a whole phrase.

A related phrase is:

• mám horečku = I have a fever

Both are possible, but mít teplotu often feels a bit closer to having an elevated temperature.

Because teplota is the direct object of mám (I have), so it must be in the accusative case.

• nominative: teplota
• accusative: teplotu

This is a very common pattern in Czech:

• mám knihu = I have a book
• mám chřipku = I have the flu
• mám teplotu = I have a fever

Since teplota is a feminine noun ending in -a, its accusative singular changes to -u.

Nejraději means most gladly, most preferably, or more naturally in English here, I prefer best / I most like to.

So:

• nejraději odpočívám = I most like to rest / I prefer to rest

It comes from:

• rád / ráda = glad, liking something
• raději = rather, preferably
• nejraději = most preferably / best of all

In this sentence, nejraději expresses what the speaker prefers to do when sick.

Because Czech often uses the present tense for repeated, habitual, or general situations, just like English does.

So this sentence means something like:

• When I have a fever, I usually prefer to rest at home and drink hot tea.

The present tense odpočívám does not have to mean only right now. It can also describe what someone normally does in that situation.

Doma means at home, and it is the normal word to use here.

So:

• odpočívám doma = I rest at home

By contrast:

• v domě means in a house/building

That is more literal and physical, and usually not what you want when talking about being at home in the everyday sense.

So for at home, use doma.

Both are correct.

• piji = more standard / a bit more formal or careful
• piju = very common in everyday spoken Czech

So you may hear:

• piji čaj
• piju čaj

Both mean I drink tea.

In a textbook sentence, piji is perfectly normal.

Because teplý (hot/warm) is an adjective describing čaj (tea), and it must agree with the noun.

Čaj is:

• masculine
• singular
• accusative
• inanimate

For a masculine inanimate singular noun in the accusative, the adjective form is the same as the nominative:

• teplý čaj

So:

• piji teplý čaj = I drink hot tea

Czech word order is fairly flexible, but the original sentence sounds very natural.

Standard version:

• Když mám teplotu, nejraději odpočívám doma a piji teplý čaj.

You could also rearrange parts for emphasis, for example:

• Když mám teplotu, doma nejraději odpočívám a piji teplý čaj.
• Nejraději odpočívám doma a piji teplý čaj, když mám teplotu.

But the original order is smooth and neutral.

A useful thing to notice is that nejraději naturally comes before the verb it modifies:

• nejraději odpočívám

Usually it suggests a general or repeated situation:

• Whenever I have a fever...
• When I have a fever...

So the whole sentence sounds like a statement about the speaker’s usual behavior when sick.

If context made it clear that the speaker was talking about one specific occasion, it could also refer to that, but by itself it sounds habitual.

Sometimes, but rest is better here.

• odpočívat = to rest
• relaxovat = to relax

When someone has a fever, rest is the more natural meaning. So:

• odpočívám doma = I rest at home

Using relax here would sound less precise in English.

Teplý can cover both warm and hot, depending on context.

So teplý čaj can mean:

• warm tea
• hot tea

In this sentence, English would usually say hot tea, but the Czech adjective itself does not always make a sharp distinction between warm and hot.