hujambo i am starting high school and i have been playing the guitar, gitaa for a while and i know a few people that can play drums and bass, so how do i start a band?

Ask them to jiunge you.

First see if wewe have permission from your parents. Then find a place wewe can practice together. It can be anywhere, like Parks, karakana of any member, au a coffee shop. After wewe have done these things decide a cool name for your band depending upon what kind of band wewe are making, and ensure that it isn't same as any other band. wewe can make a Rock and Roll, Emo, Punk, au any other genre wewe like. Then after wewe have decided the name start practicing. First as beginners wewe can sing covers of your fav songs and later wewe can write songs on your own. To popularise your band wewe make band posters and paste it on public places so that people would come to know about it. wewe can organise small shows at occasions like your friend's birthday au some get-together parties.
So, get going and rock it!! I think this will help you. :)