Real consent is mutual and sure. It is not muted, frail, hesitant, or afraid. It is never uncertain, assumed, or silent.
Consent cannot be gained through manipulation, intimidation, or threatening behaviour. A person who is intoxicated with alcohol or drugs can't give consent. Consent cannot be given by a person who is passed out or asleep. Consent must be continuous and can be withdrawn at any time during sex.
Sex without enthusiastic consent is not sex at all. It's sexual assault or rape.
Make sure everyone is into it before you get into it.