How do i tell someone i think have depression and may be suicidal im 12?

Find an adult you trust (maybe even the doctor) and just say it out straight. If they are someone who cares about your well-being, they will not make fun of you. If you don't have anyone like that, you can talk to one of your closest friends and ask them to help, and see if they have an adult they trust that can help you. You should never let yourself suffer in silence, goodness knows- that's gotten my own friends in bad places. Don't feel bad though, 12 year olds can be fickle and cruel. It is something that comes with childhood and never really goes away, but there are always also lots of kind people who will love you even momentarily as a stranger. Never be afraid to ask for help.