请问don't,doesn't,aren't的用法?

请问don't,doesn't,aren't的用法?
aren't属于be动词是在句子中没有动词的时候用的?　那don't 和doesn't 都是在句子中有动词的时候用的吗?
比如：我们不在同一层楼．　　可以说：we aren't on the same floor.　也可以说：we don't on the same floor.
麻烦解答的能给我理一下判断实用don't ,doesn't,aren't 的规律,