Das Auto fährt jetzt weg.

Because Auto is a neuter noun in German. Its basic singular article is das.

• das Auto = the car
• der is for many masculine nouns
• die is for many feminine nouns

In this sentence, das Auto is also the subject, so it is in the nominative case.

The verb is fahren = to drive / to go by vehicle. In the 3rd person singular present tense, it changes its stem vowel:

• ich fahre
• du fährst
• er/sie/es fährt

So das Auto fährt means the car drives / is driving.

This is a common kind of stem change in German verbs.

Because the full verb is wegfahren, which is a separable verb.

In a normal main clause, German separates it like this:

• Das Auto fährt weg.

What happens is:

• the conjugated part (fährt) goes to the usual verb position
• the prefix (weg) moves to the end

So although you see fährt ... weg, you should understand it as the verb wegfahren.

In this sentence, it functions as part of the separable verb wegfahren.

On its own, weg often means away or gone, but here it combines with fahren to give the idea drive away / leave by vehicle.

So learners should mentally connect:

• fährt ... weg = wegfährt
• base verb: wegfahren

German main clauses usually follow the verb-second rule. That means the finite verb must be in the second position.

Here the sentence is organized like this:

1. Das Auto = first element
2. fährt = finite verb in second position
3. jetzt = time expression
4. weg = separable prefix at the end

So the structure is completely normal for German.

Yes. That is also correct.

German lets you move different elements to the first position for emphasis, as long as the finite verb stays in second position:

• Das Auto fährt jetzt weg.
• Jetzt fährt das Auto weg.

The meaning is very similar, but the second version emphasizes now a bit more.

Jetzt usually means now or right now.

In this sentence, it tells you the action is happening at this moment or at this point. Depending on context, it can sometimes also feel like now, as opposed to earlier, but the basic meaning is simply now.

German nouns sometimes change form in different cases, but Auto does not change here.

You just see:

• das Auto in the nominative singular
• also often das Auto in the accusative singular

So in this sentence, Auto stays the same because it is the subject and does not need any special ending.

When a separable verb is used in certain structures, it often becomes one word again.

For example:

• Ich weiß, dass das Auto jetzt wegfährt.
• Das Auto will jetzt wegfahren.

So:

• in a main clause: Das Auto fährt jetzt weg
• in a subordinate clause: ..., dass das Auto jetzt wegfährt
• in the infinitive: wegfahren

This is an important pattern with separable verbs.

Not necessarily. German often uses fahren with vehicles to describe movement, even when no driver is mentioned explicitly.

So Das Auto fährt jetzt weg simply means the car is leaving / driving away. It does not automatically mean the car is literally self-driving. The sentence just focuses on the car as the thing moving.