Well you have to get out there and meet people. Seriously. If you are a cool guy and you are meeting a lot of people, then there is no way you can't make friends. Get a hobby, go to some school clubs, get into the school sports teams, just meet as many people as possible.
You want to do something with people outside of school, get their numbers, invite them out for a drink or something like that, or wait until you are accepted into a social circle and they will start inviting you out.
This is the easy part, the hard part is being someone who has social value to give to a group of friends and not being someone who will just drain value. on't be depressed, be upbeat, sociable and fun. Get confident.