It goes beyond no means no.
In this day and age, we need to relearn what consent is. In the Netflix show 13 Reasons Why, one of the main characters (Bryce) said: "I could tell she wanted it and she didn't exactly say no." That's such a young guy way of thinking, and some men never grow out of that. They can't wrap their minds around why women don't want sex with them all the time. Men also don't understand why women don't want sex to be the focus of a relationship. You will not die if you don't get sex when you want it. Not every girl is going to want you... shocker, I know. Now I know not all men think the way I just described. There are decent men out there. It's not just men that need to learn about consent either, we all do.
So what is consent? Consent is the permission or agreement to do something or for something to happen. It is educated and direct. A person can also change their mind about what they gave consent to. You have not gotten consent unless you have actually asked and gotten an answer. "I guess" is not a yes and silence (or inaction) is not a yes. A person has to say something along the lines of yes or sure. Although consent doesn't have to be verbal in some cases. If in your act your partner pushes you away, removes your hand, or tenses, these are some of the many signs of no.
You have to tell your partner exactly what is going to happen to them before you do it to them. If this is a BDSM situation, then you have to describe what you will be doing to them or educate them if the act is new to them. If they don't understand, then you have to show them an example and your partner can't give you consent until they understand the act.
Once consent is given it can be changed. Yes, your ego may be bruised and you may be blue (or pink) balled. Yes, girls get blue balled, it's called pink balled. You will get over it and life will move on. If your partner says stop, you have to stop. If they say stop and you don't, it's still the same as if they have never said yes in the first place. If your partner gives you consent for one act one time, their consent is for that one act for that one time.
Consent can't be given if someone is drunk, high, or not in their right mind. They also can't give consent if they are unconscious. To get consent they must be sober, in their right mind, and conscious. There are some people who are into consensual un-consent, which is fine, you just have to get consent first. People are also into drunk or high sex or play, and again that's fine, just get consent first.
The second you don't get consent or it changes, things need to either not happen or stop happening. If you are over 18, you need to be participating in acts that are sexual in nature with other people who are 18 and older.
Don't feel like you can't say no or push someone away. You have to feel comfortable with what is happening to you or what is about to happen to you. You shouldn't feel like you have to do something to keep someone in your life. There is no pressure to do anything that you don't want to do.
If you don't give consent, push them away. Any act that happens after that is rape or assault. If rape or assault occurs, then tell someone you trust.