Když je ráno zima, vezmu si bundu a jdu pěšky do školy.

Když introduces a subordinate clause and here it can be understood as when or if, depending on context.

In this sentence, it describes a repeated situation:

• Když je ráno zima... = When/If it’s cold in the morning...

A useful rough guide:

• když = when for time, and often also if in everyday repeated situations
• jestli = more specifically if/whether
• pokud = more formal if/provided that

So here když is very natural.

Czech often uses impersonal expressions for weather and general conditions.

So:

• Je zima. = It is cold.
• Je horko. = It is hot.
• Prší. = It is raining.

English needs a dummy subject it, but Czech usually does not.

Here zima does not mean winter. It means cold in the expression je zima.

So:

• zima = winter as a noun in some contexts
• je zima = it is cold

This is a very common Czech expression, and learners just have to get used to it as a set phrase.

Ráno means in the morning or morning.

In this sentence it works adverbially:

• Když je ráno zima... = When it’s cold in the morning...

Czech often uses time words like this without a preposition. English says in the morning, but Czech can simply say ráno.

Because Když je ráno zima is a subordinate clause, and in Czech subordinate clauses are normally separated by a comma.

So the structure is:

• subordinate clause: Když je ráno zima
• main clause: vezmu si bundu a jdu pěšky do školy

This comma is required in standard Czech.

This is mainly about aspect.

• vzít / vezmu = perfective
• brát / beru = imperfective

Vezmu presents the action as a single complete action: I take/put on/grab a jacket.

Because perfective verbs do not normally have a true present meaning in Czech, vezmu often has a future-like sense:

• vezmu si bundu = I’ll take/put on a jacket

In a sentence like this, it means something like:

• When it’s cold in the morning, I take / I’ll take a jacket

If you said beru si bundu, it would sound more like a repeated habit or ongoing usual behavior. That can also work in some contexts, but vezmu si is very natural when the speaker imagines each situation as one complete event.

Si is a reflexive/dative clitic, and here it means something like for myself.

So:

• vezmu bundu = I take a jacket
• vezmu si bundu = I take a jacket for myself / I put on or grab a jacket for my own use

With clothes, vzít si often corresponds to English put on, take, or grab, depending on context.

In this sentence, vezmu si bundu is naturally understood as:

• I put on a jacket or
• I take a jacket

Because bundu is the accusative singular form of bunda.

Bunda is a feminine noun, and as a direct object it changes:

• nominative: bunda
• accusative: bundu

Here it is the object of vezmu si:

• vezmu si co? → bundu

So this is a normal case ending change.

This is a very common learner question, because Czech has two different kinds of go/walk verbs.

• jdu = I go / I am going, one concrete trip, one direction
• chodím = I go / I walk regularly, habitually, back and forth in general

In this sentence, jdu pěšky do školy presents the school trip as the concrete action that happens in that situation.

If you said chodím pěšky do školy, that would emphasize a general habit:

• I walk to school

So:

• jdu = this trip / each such occasion as a concrete event
• chodím = habitual routine in general

Both can make sense in different contexts, but jdu is fine here.

Yes, but the nuance changes.

• jdu = I go / I’m going
• půjdu = I will go

Půjdu would sound more explicitly future:

• Když je ráno zima, vezmu si bundu a půjdu pěšky do školy.

That is possible, especially if you are talking about a future occasion. But jdu sounds more immediate and natural in a general everyday statement.

Pěšky means on foot.

So:

• jdu pěšky = I go on foot / I walk

It is an adverb, so Czech does not need a preposition here. English uses a phrase (on foot), but Czech uses the single word pěšky.

Because do is the preposition used for motion to/into a destination, and it requires the genitive case.

• škola = school
• genitive singular = školy

So:

• do školy = to school

This is a very common pattern:

• do města = to the city
• do práce = to work
• do školy = to school

Because k and do do not mean the same thing.

• do školy = to school, into the school / to the destination school
• ke škole = toward the school, up to the school, near the school

If you are talking about your destination as a student, do školy is the normal choice.

It can be interpreted either way depending on context, but most naturally it sounds like a general repeated situation:

• When it’s cold in the morning, I take/put on a jacket and walk to school.

However, Czech also often uses the present tense after když for future meaning. So in the right context it could also mean something like:

• When it’s cold tomorrow morning, I’ll put on a jacket and walk to school.

Without extra context, learners should probably understand it as a habitual/general statement.

Yes, Czech word order is fairly flexible, but different orders change the emphasis.

The given version is neutral and natural:

• Když je ráno zima, vezmu si bundu a jdu pěšky do školy.

For example:

• Když je zima ráno... is possible, but it sounds a little different in emphasis.
• Jdu do školy pěšky is also possible instead of jdu pěšky do školy.

So the sentence is not the only possible order, but it is a very normal one.