What does it mean when a boy is afraid of you. and afraid to talk to you?

It is probably one of four things:

First, he could be actually physically afraid of you (like as he would be afraid of a twenty foot crocodile), though this is highly unlikely-unless your one of those female body builders...

Secondly, he could be afraid you want to have a relationship with him when he doesn't want to, either because he doesn't love you or doesn't think he is ready for a relationship yet.

The third (and most common) reason a boy would be afraid to talk to you is that he is hopelessly, head-over-heals in love with you. He is probably afraid you'll turn him down if he makes any advances and is afraid his relationship with you will worsen if proclaims his love for you.

And lastly, he could be just downright shy in general and has no feelings for you either for good or for ill.

If you love him, then give him hints of your love (not to subtle, guys are very unobservant) and don't play "hard to get" (that will probably discourage any motivation he previously had).

If you do not love him, then give him no reason to believe that you would desire a relationship with him. And if he asks you out, don't give him a wishy-washy answer. Give him a gentle but unmistakable "no".

If you have no idea what your feelings for him are, give him time and try not to confuse him. If he asks what are your feelings for him simply tell him that you honestly do not know.