What do I do after starting period?

Please help! I just went to the bathroom to.. well, pee. But when i pulled down my underwear I saw blood. Now, I'm only 11, and I know it's my period, but today is July 1st and tomorrow I am supposed to go to Jackson to go to my uncle's and party for Fourth Of July. I just started, it's not heavy, and I LOVE to swim. I just got off the phone with my mom. She says it's up to me on what I want to do... I'm not sure if a tampon would be necessary for my young age... or would it? Please help, I know this is private, but I don't know what I should do!!! :(