how do I birth control?

Hello eve girls! I lost my virginity to my now ex boyfriend a couple months ago. I wanted to get on the pill but didn't know how. Before we unexpectedly broke up I turned 18 so I knew that it could be easier for me to get birth control pills. A week after we broke up, I saw my doctor for a UTI and she also gave me a prescription for birth control pills, even though I had broken up with my boyfriend and wasn't having sex at the moment. I have the prescription hidden in my room, and all I would have to do is go to Costco's pharmacy and pay for the pills in cash (no problem bc I have a job). It's been about a month since my break up and today I'm going on a date with this new guy I met. I honesty didn't expect to meet someone else so quickly. Anyways, i think it would be logical to start the pill now. But I'm confused on when to start taking it. I got my period this Sunday (the 11th) but I was told you're supposed to start taking the pill before you start your period? Or am I getting the info confused? I know that once I start it will take a week for it to start actually working and that I've gotta take it at the same time every day for it to work properly. Help needed! Explain this magic pill to me!