Birth control questions

Ashley

So I'm going to an appointment I set up for getting on birth control and it's on the 17th and my questions are, will I get out on it that day? And if so I am supposed to start my period that day so would I still be able to take it and would it stop my period or what would happen? And what are the short term side effects of it? My one friend was going around saying it would help me gain weight and would make me very emotional and stuff