Když jsem na rohu a nevím, kam jít, dívám se do mapy.

Czech often drops subject pronouns because the verb ending already shows the person.

• jsem = I am
• nevím = I don’t know
• dívám se = I look / I am looking

So já is not necessary here. You could add it for emphasis, but the neutral version usually leaves it out.

Když means when here. It introduces a subordinate clause:

• Když jsem na rohu a nevím, kam jít...
  = When I’m at a corner and don’t know where to go...

Depending on context, když can also sometimes mean if in everyday Czech, but in this sentence when is the most natural understanding.

The sentence is describing a general or repeated situation, not one specific moment. Czech uses the present tense for this just like English can:

• When I’m at a corner and don’t know where to go, I look at a map.

So this is a habitual or typical action: whenever that situation happens, this is what the speaker does.

Na rohu means at the corner, usually a street corner.

The noun is roh = corner. After na in a location meaning, Czech uses the locative case:

• roh → rohu

So:

• na rohu = at/on the corner

Here na does not mean literal English on. It is just the normal Czech preposition used in this expression.

Because kam asks about direction or destination: where to?

• kam = where to
• kde = where in the sense of location

Since jít means to go, the sentence needs the idea of destination:

• nevím, kam jít = I don’t know where to go

Using kde would not fit well with jít, because going involves movement toward somewhere.

Because it depends on nevím:

• nevím, kam jít = I don’t know where to go

Czech often uses question word + infinitive in this kind of structure:

• co dělat = what to do
• kam jít = where to go
• jak začít = how to start

You could also say:

• nevím, kam mám jít = I don’t know where I’m supposed to go

But nevím, kam jít is shorter and very natural.

Dívat se means to look or to watch. It describes an intentional action.

• dívám se = I’m looking
• vidím = I see

So in this sentence, the speaker is actively consulting the map, not just accidentally seeing it.

Because dívat se is the normal dictionary form of the verb. The se is part of the verb.

• dívat se = to look
• dívám se = I look / I’m looking

Many Czech verbs use se or si, and English learners often just have to learn them as part of the verb. Here, dívat without se would not mean the same thing in normal usage.

Because the preposition do always takes the genitive case.

The noun is:

• mapa = map

Its genitive singular form is:

• mapy

So:

• do mapy = literally into the map, but idiomatically at the map / in the map

That is why the ending changes.

Yes, it is very natural, especially when you mean consulting a map for information.

Czech often uses do with things you look into for guidance or information, such as maps, books, notes, or timetables.

So:

• dívám se do mapy suggests I check the map / I look at the map to find my way

You may also hear dívat se na mapu, but do mapy is especially idiomatic when the map is being used as a source of information.

Because Czech uses commas to separate subordinate clauses.

The structure is:

• Když jsem na rohu a nevím, kam jít, = subordinate clause
• dívám se do mapy. = main clause

There is also another subordinate part inside the first one:

• nevím, kam jít

So the commas mark clause boundaries:

1. before kam jít
2. after the whole opening když-clause, before the main clause

This is standard Czech punctuation.