My family being mean and I want to leave forever. How do I put myself up for adoption so my friends family can adopt me?

You go to Court and ask to be emancipated - once you are emancipated (your own person), then the other family can adopt you if they wish. The other family could also go to Court, prove the abuse, and ask for guardianship of you. There will undoubtedly be a Court battle but when there is evidence it is possible.

In order to be emancipated you must be 100% self supporting (employed), have a place to live (not with family or friends) and either have your education completed or have plans to do so.

Or you could simply discuss the situation with a third party, uninvolved adult (clergyperson, Physician, social worker, teacher) and try to resolve it that way OR you and your family could consult with a third person and find out why they are being mean.

For legal purposes - what mean things are they doing to you?

One of the most important things is how old are you?

How do you this as one of the most important factors?
He's obviously under the age of majority and that's what matters.