Hello I need some advice.

My son is 4 he'll be turning 5 this June. My son has no stranger danger instilled into him. How do I go about teaching him stranger danger?

Another one I have a worry about my son being bullied or allowing people to bully him because he is to nice or doesn't know how to stick up for himself.

How as a mother would you combat this? How would you teach your kids not to speak to strangers and to stick up for themselves.