If two or more people have agreed to engage in sexual activities, there should be a discussion about boundaries, and what types of sexual activities are okay. If, for example, one partner is comfortable with vaginal penetration but not anal, and that boundary is crossed, this is a clear violation of consent.
Discussing sexual interests or wanting to try new things doesn't have to be an awkward conversation. Still, it should be a conversation, and consent must be given before anything further is attempted. A partner saying, "I'm open to trying that" or "Yeah, let's do it," is an affirmation of consent. Keep in mind an involved party can change their mind at any point, and boundaries need to be respected.