Our last topic was about the prepositions:
in, an, auf, and bei.
Ich bin im Büro. (inside)
Ich warte an der Bushaltestelle. (at, near)
Ich sitze auf dem Balkon. (on → open space)
Ich bin beim Arzt. (at someone's)
We use those when the question we answer is WO?
When the question is WOHIN?, we use other prepositions. English does this as well, look:
I'm at the office. vs. I'm going to the office.
The difference is that English uses "to" pretty consistently for almost every direction, no matter the destination and German is once more, very precise about details. We have broken down the cases for you.
If you go inside a place: IN + accusative
but: "Ich bin im Restaurant"
but: "Ich bin im Supermarkt"
but: "Ich bin in der Kneipe"
If you are not going inside, but only to the entrance or you just want to state your direction in a general way: ZU + dative.
Zu is usually used when we intend to say we are not going inside the place but only reaching the entrance or a nearby location. Most commonly you would use zu when you use fahren.
If you are going (or driving) to someone's place: ZU + dative
(That makes sense because you can't go inside someone like they were a building.)
I'm going to your place now.
I'm going to the doctor's.