You use perhaps to express uncertainty, for example, when you do not know that something is definitely true, or when you are mentioning something that may possibly happen in the future in the way you describe.

You use perhaps in opinions and remarks to make them appear less definite or more polite.

You use perhaps when you are making suggestions or giving advice. Perhaps is also used in formal English to introduce requests.

You can say perhaps as a response to a question or remark, when you do not want to agree or accept, but think that it would be rude to disagree or refuse.