Learn German: Wohin fährt der Bus? - Where is the bus driving to?

Wohin means "where to" and is used to ask about a destination or movement toward a place. Wo just means "where" (a fixed location). Since the bus is traveling to a destination, we use Wohin.

Why does the verb fährt come before the subject der Bus?

In German questions that start with a question word (like Wohin), the verb always takes the second position. The subject (der Bus) has to come right after the verb.

Why does the verb fährt have an umlaut (the two dots over the a)?

The base verb is fahren (to drive). For "he, she, or it" (like der Bus, which is a masculine noun), the "a" changes to an "ä". This is a common vowel change for some irregular verbs in the present tense.

Can I use the verb gehen (to go) and ask "Wohin geht der Bus?"

Not in German! The verb gehen specifically means to walk or go on foot. Because a bus travels on wheels, you must use fahren (to drive/ride).