Když jdu do práce, beru si s sebou telefon i hodinky.

Když means when.

It introduces a subordinate clause: Když jdu do práce = When I go / am going to work.

In Czech, subordinate clauses are normally separated by a comma, so the comma here is required.

This is a very common question because Czech has two different verbs where English just has go.

• jít / jdu = to go in one direction, to be going, to be on the way
• chodit / chodím = to go regularly, habitually, back and forth

So:

• Když jdu do práce means when I’m going to work / when I’m on my way to work
• Chodím do práce means I go to work regularly or even I have a job and go there

In this sentence, jdu focuses on each individual trip to work, not just the general habit.

Do takes the genitive case.

So práce here is genitive singular:

• nominative: práce
• genitive: práce

They happen to look the same in this noun.

Do práce means to work or literally into work / to the workplace.

The verb is brát si, which often means to take for oneself or simply to take in a natural, personal sense.

Here, si is a reflexive dative pronoun, roughly meaning something like for myself or with me, although you usually do not translate it directly into English.

So:

• beru telefon = I take the phone
• beru si telefon = I take the phone for myself / I’m taking the phone along

In this sentence, beru si sounds natural and idiomatic.

S sebou means with oneself, along, or along with me/you/etc.

It is very common with verbs like brát and vzít:

• brát si s sebou = to take along
• vzít si s sebou = to take along

So:

• beru si s sebou telefon = I take my phone with me / I bring my phone along

They are related, but they do not do exactly the same job.

• si is part of the verb phrase brát si
• s sebou adds the idea of along with oneself

Together, beru si s sebou is a very natural Czech expression for I take ... with me.

So even if it feels repetitive from an English point of view, in Czech it is normal and idiomatic.

They are in the accusative case because they are the direct objects of beru.

• telefon = accusative singular
• hodinky = accusative plural

For these nouns, the accusative looks the same as the nominative.

In Czech, hodinky is normally a plural-only noun when it means a wristwatch.

So even if you mean one watch, Czech still uses the plural form:

• Ty hodinky jsou nové. = That watch is new.

This is similar to how English has nouns like scissors, which are grammatically plural even when they refer to one object.

Here i means something like also, as well as, or both.

So:

• telefon i hodinky = the phone and the watch as well / both the phone and the watch

It is close to a (and), but i often gives a feeling of addition or emphasis.

Compare:

• telefon a hodinky = phone and watch
• telefon i hodinky = phone and also watch / both phone and watch

Brát is the imperfective verb, and vzít is the perfective partner.

Because this sentence describes a repeated or habitual action, Czech normally uses the imperfective:

• Když jdu do práce, beru si s sebou telefon i hodinky. = Whenever I go to work, I take my phone and watch with me.

If you were talking about one future occasion, you might use the perfective:

• Až půjdu do práce, vezmu si s sebou telefon i hodinky. = When I go to work, I’ll take my phone and watch with me.

Grammatically, the verbs are in the present tense, but the meaning is habitual.

Czech present tense often describes regular actions, not only what is happening right now.

So this sentence means something like:

• Whenever I go to work, I take my phone and watch with me.

It does not have to mean that the speaker is going to work at this exact moment.

Yes. Czech word order is flexible, and changing it changes emphasis more than basic meaning.

The given sentence is neutral and natural:

• Když jdu do práce, beru si s sebou telefon i hodinky.

You could rearrange parts, but the focus would shift. For example:

• Telefon i hodinky si beru s sebou, když jdu do práce.

This gives more emphasis to telefon i hodinky.

For learners, the original word order is a very good standard model.