don't walk, uber, you'll have hella sore legs. don't go to beaches they're really cold up here, if you want beaches go to socal.
pier 34/fisherman's wharf is fun, especially on the 4th if you're not already going. lombard street, painted ladies, alcatraz (if you can get reservations, i think in the summer they're wicked backed up) are all fun. if you like hiking there's plenty of hiking in the east bay, grizzly peak etc. given that you're 14 (profile correct or nah?) i'll presume nightlife isn't really an option lol
land's end is pretty cool i've heard. walking the golden gate bridge can be fun. there are good boat tours in the bay too.
also there are hella art museums around here. sf moma is pretty new. just look around for something that interests you.
oh and if you're into sports at all i've heard giants games are really fun. don't know if they're at home at all while you're here tho
and i'd def recommend at least walking through the castro LOL if not to actually go there it's a fun time in general. obv if you're 14 it might be a little weird with all the love shops and all esp if you have parents but whatevs
honestly there's a little bit of everything, you just have to find what you want to do