The meaning is pretty much the same, but "it doesn't matter" can stand alone as a sentence. In your first example, both are complete sentences; however, the second should use a semicolon rather than a comma to connect the two independent clauses. - No matter who you are, you should respect your teacher. - It doesn't matter who you are; you should respect your teacher. - No matter if you are short or tall. ー this is not a complete sentence as there is no verb. - It doesn't matter if you are short or tall. ー this is fine as is. I hope that explanation helps. Good luck with your studies.

No matter if you are short or tall. this is not a complete sentence, but the other is. The 'it' is the subject in the second, it refers to the reason why it doesn't matter. If you use 'No matter why...', you need to follow it with something that is related to what you have said. e.g. No matter how much you learn, there is no substitute for practice.