N は N に あります/います

猫は部屋にいます。

Neko wa heya ni imasu.

The cat is in the room.

When the subject is known the sentence gives the location — the reverse of に…が

トイレはどこにありますか。

Toire wa doko ni arimasu ka.

Where is the toilet?

The single most useful question to have ready

先生は教室にいます。

Sensei wa kyōshitsu ni imasu.

The teacher is in the classroom.

The answer when someone is looking for a person