How to go from best friend to a relationship.?

Me and this girl have been great friends for awhile, and she likes me. She's told before that I'm cute and stuff, but I've just never been super interested in her as my girlfriend until recently. Maybe I'm just a typical dumb guy, but we were texting the other night and she was telling me how at one of my schools football games thy called my name on the speaker and she was like yeah! And the color guard coach asked if I was her boyfriend and she said no, but he's praticaly my best friend, and that the coach was like sure..... To me at least I think she was I don't know maybe trying to tell me somethingI'm just not sure how I should necessarily go about it. We've done stuff together but never like an official date or anything. How do I differentiate from just doing stuff to like an actual date, and how/ when should I ask her to be my girlfriend?