Yes, sexuality is a big topic to have to reduce down to one label. You sound like you are young, but let me tell you that even when you are older it can still feel like you are giving people too much and too little information at the same time.
First of all, remember that you don't have to say anything to anyone. It's your life and your business.
Here's one way to think about it: Do you want your friends to introduce you to cute boys or cute girls? Or both?
Don't feel like you have to put yourself in a box (being too restrictive), or needing to explain complicated feelings and experience (too much information).
Just give them what they need to help you take your next step. If you want to meet boys, then tell them you are gay. If you like both, then tell them you are bisexual. Or tell them you are straight, if you just want to date girls.
Don't get pulled into the whole "Am I 100% gay?" inner dialog. Who knows? Who ever knows? As the years go by it will become more clear. The only relevant question is who do you want to date next? If you change your mind next year, then that's OK. Other than your family and closest friends, nobody really cares about the details of your sexual complications. They just don't want to be embarrassed by saying the wrong thing.
Coming back to the subject of telling people at all - you have the most power when you take the initiative and set people on the right track. That is, IF you are comfortable with yourself and you feel the environment is safe. It can sometimes take a while to get to that comfort level - which is OK. And depending on where you live, society may be welcoming, indifferent, or hostile to your sexuality. Those are important factors to consider.
Your safety, both emotionally and physically, comes first. After that its time to get some dates going.