Der Fahrer stoppt das Auto.

the car

Breakdown of Der Fahrer stoppt das Auto.

• der Fahrer: the driver
• stoppen: to stop

Questions & Answers about Der Fahrer stoppt das Auto.

Why is Der Fahrer capitalized and what role does Der play?

In German every noun is written with a capital letter, so Fahrer gets a capital F. The word Der is the definite article (the) in the masculine singular nominative case, marking Fahrer as the subject of the sentence.

Why is das Auto in the accusative case, and why is its article also das?

Auto is a neuter noun. In German the definite article for neuter singular is das in both nominative and accusative. Here das Auto is the direct object (accusative case), but the form of the article doesn’t change.

How is the verb stoppt formed from the infinitive stoppen?

Stoppen is a regular (weak) verb. For third-person singular (he/she/it) in the present tense you drop the ending -en and add -t:
stoppen → stopp​t → stoppt.

Is stoppen a separable verb? If not, why doesn’t it split?

No, stoppen is a simple, inseparable weak verb. Only verbs with prefixes like an-, auf-, mit- etc. can be separable. Since stoppen has no separable prefix, it stays together in all tenses and moods.