Die Straße ist zu, darum fahren wir heute nicht in die Stadt.

In this sentence, zu is a common everyday adjective meaning closed or shut.

So:

Die Straße ist zu. = The road is closed.

You will often hear this with sein:

• Der Laden ist zu. = The shop is closed.
• Die Tür ist zu. = The door is shut.

This is a different use of zu from:

• the infinitive marker, as in zu machen
• the preposition zu meaning to
• zu meaning too

German uses the same word in several different ways, so the meaning depends on context.

They are very similar, but not exactly the same in tone.

• zu is shorter and more everyday
• geschlossen is a bit more formal or explicit

So both can mean that something is not open or not accessible.

For a road, German also very often uses gesperrt, which is even more specific:

• Die Straße ist gesperrt. = The road is blocked/closed to traffic.

So in real life, for roads, gesperrt is often the most natural word. But zu is perfectly understandable and very common in casual speech.

Darum means therefore, for that reason, or that’s why.

It refers back to the first clause:

• Die Straße ist zu = the reason/situation
• darum fahren wir heute nicht in die Stadt = the result

So the logic is:

The road is closed, therefore we are not driving into town today.

It is a consequence word, not a because word.

Because German main clauses follow the verb-second rule.

That means the finite verb has to be in the second position. If darum comes first, then the verb must come next:

• Darum fahren wir ...

not

• Darum wir fahren ...

You can think of it like this:

1. darum
2. fahren
3. wir

This same pattern happens with many other words at the beginning of a clause:

• Heute fahren wir nicht in die Stadt.
• Deshalb bleiben wir zu Hause.
• Morgen kommt er.

Yes, but the structure changes.

With weil:

• Wir fahren heute nicht in die Stadt, weil die Straße zu ist.

Here weil means because, and the verb goes to the end of the subordinate clause: ist.

With deshalb or deswegen:

• Die Straße ist zu, deshalb fahren wir heute nicht in die Stadt.
• Die Straße ist zu, deswegen fahren wir heute nicht in die Stadt.

These work almost the same way as darum.

With denn:

• Wir fahren heute nicht in die Stadt, denn die Straße ist zu.

Here denn also means because, but it does not change the word order of the second clause.

So:

• darum / deshalb / deswegen = result words, with normal main-clause inversion
• weil = subordinate clause, verb at the end
• denn = coordinating conjunction, no inversion

Because this is the most neutral and natural word order.

Wir fahren heute nicht in die Stadt means something like:

We are not going into town today.

In German, nicht usually comes before the part being negated, or fairly late in the clause. Here the sentence is naturally organized like this:

• wir
• fahren
• heute
• nicht
• in die Stadt

If you said nicht heute, that would sound more contrastive, like:

• Wir fahren nicht heute in die Stadt.

This suggests:

not today, but maybe another day

So heute nicht is neutral; nicht heute is more emphatic or contrastive.

Because in can take either the accusative or the dative, depending on meaning.

• in die Stadt = movement into the city/town → accusative
• in der Stadt = location in the city/town → dative

So:

• Wir fahren in die Stadt. = We are going into town.
• Wir sind in der Stadt. = We are in town.

This is a very important German pattern:

• wohin? where to? → accusative
• wo? where? → dative

Fahren is used when traveling by some kind of vehicle, or more generally when going somewhere by transport.

So it can mean:

• drive
• ride
• go by car, bus, train, bike, etc.

Gehen is specifically go on foot or walk.

So:

• Wir fahren in die Stadt. = We go/drive into town.
• Wir gehen in die Stadt. = We walk into town.

In everyday German, fahren is very common when the exact mode of transport is not the main point.

Yes, literally it means into the city/town, but in everyday German it often means something more natural in English like:

• into town
• to town
• into the city center

So in die Stadt fahren is a very common expression. It often means going from somewhere outside the center into the town or city area for shopping, errands, meeting people, and so on.

So even though the literal translation is useful, the everyday sense is often just go into town.

ß is called Eszett or scharfes S. It is pronounced like ss, not like an English z.

So Straße sounds roughly like:

SHTRAH-suh

The ß itself is just an s sound.

Also, in Switzerland, people usually write ss instead of ß, so you may see:

• Strasse

That is the same word.

Because this sentence contains two main clauses:

• Die Straße ist zu
• darum fahren wir heute nicht in die Stadt

Darum is not a conjunction like und or denn. It is a conjunctive adverb, which means it belongs to the second clause and takes up the first position there.

So if you keep both parts in one sentence, the comma separates the two clauses:

• Die Straße ist zu, darum fahren wir heute nicht in die Stadt.

You could also write:

• Die Straße ist zu. Darum fahren wir heute nicht in die Stadt.

That is also correct.