Sexual consent means agreeing that you agree to a specific sexual activity. So getting or giving consent is an ongoing process. Always remember:
Just because a person says yes to one type of sexual activity doesn't mean that they agree to everything. If someone shows a sexual interest one time it isn't an open invitation to have sex later. Any sexual activity without consent is sexual assault and that's a crime.
Being involved in a sexual relationship requires clear and direct communication. Each person in a sexual relationship is responsible for clearly giving and clearly receiving consent.
There's more information about how old you need to be to give consent in the "Sex and the Law" part of this website.