You can confirm an idea with this expression.
For example, if you're dirty and dressed badly, you can ask someone:
I look horrible, don't I?
Use "don't I?" with most verbs. However, if the verb of the sentence is "am", use "aren't I?". When the verb is "can", use "can't I?" And with "will", use "won't I":
I'm late, aren't I?
I can be a little annoying sometimes, can't I?
I'll be the only girl there, won't I?
When you're using this expression confirming what you already think, your voice goes down at the end of the sentence. If you're really not sure about the answer, your voice goes up at the end.