I'm a rookie and i'm scared that ranked means that it is for more experienced.

nah, brackey's jams are all for beginners to experienced people, im pretty sure it just means everyone's submission to the jam will be ranked. ex: 1st place 2nd place or 200th place and so on, based on how many people vote for your game.

I am only 12 and I don't care about rank. All that matters is your participation.  Game jams are for fun and learn.