Learn Russian: Почему ты хочешь стать водителем?

When you use the verb стать (to become) to talk about a profession or a change in status, the noun that follows must be in the instrumental case. You cannot use the dictionary form (водитель).

How exactly does водитель change to водителем?

Водитель is a masculine noun that ends in a soft sign (-ь). To form the instrumental case for this type of noun, you drop the -ь and add the soft ending -ем.

Why use the perfective verb стать instead of the imperfective становиться?

When talking about future career goals, Russian typically uses the perfective стать because the focus is on the final result—achieving the status of a driver—rather than the ongoing process of learning or training.

I know хочешь means "you want", but is it a regular verb?

Not entirely! Хотеть (to want) is a tricky mixed verb. In the singular forms like ты хочешь, it uses standard "E-type" endings. However, if you were asking a group, the plural form switches to "I-type" endings: вы хотите.