Explain what you're doing
The GM tells you what might happen
They will list one or more Outcomes, which you can mentally divide into benefits, the thing(s) you're trying to do (usually just one thing), and consequences, the things you are trying to avoid. Those are the same thing mechanically, an Outcome, but people tend to think about them seperately.
Often, you'll just get conquences, because your character is so good that the GM thinks you are unlikely to fail. Or just get benefits, because nothing bad is going to happen but the GM wants to see how well you succeed.
If you don't like what the GM has offered, you may want to pick a different action, or do nothing at all. You don't ever have to do anything, although sometimes you will already be in danger, and if you do nothing, the bad thing will happen.
You figure out what to roll
For an Action Roll, you start with 1d in each dot you have in that Action, if any.
If you have more than one Outcomes, you add a 1d for each additional Outcome after the first. Then you add any bonus dies that might apply.
Then you roll that dice pool, giving you a pool of result dice. (Or, before that, you do something that make things better before you roll.)
Assigning results to outcomes
You take each Outcome and assign a different result die to it, and discard any extra. The meaning of the rolls:
1-3 - Failure - You have failed. Whatever you were trying to do has not worked, or whatever you were trying to avoid has not been avoided.
4-5 - Partial Success - You succeeded, but not perfectly. What you were attempting did mostly work, or you partially avoided the problem.
6 - Success - You succeed perfectly. You have done what you were trying to do, or avoided completely the bad.
And the GM tells you the results, narratively. (Or, before that, you do something to make things better after you roll.)
Alternately, if you are in Lesser Peril, and you rolled badly, you can just stop what you were going to do before you do it, if you want. Narratively, you see the upcoming failure and realize your plan will not work. Although this means you cannot try it again.
Gameplay
Lucas: I want to take the knife from the guy waving it around.
GM: That's tricky from where you are, so I'm going to make you roll for that. You also might cut yourself in the struggle. That feels like Assault.
| Assault, two dot, two outcomes, three dice | |
| Disarm the knife from the guy waving it around | |
| Not cut myself on knife |
Lucas: Sounds good. I have 2 dot in that, two outcomes, so rolling 3d. And got 3, 1, and 5. Two failures and a partial. That's not good. I do need to disarm him, so I'll put the partial success in that, and a failure in the 'not getting hurt'.
| Disarm the knife from the guy waving it around (partial success) | |
| Not cut myself on knife (failure) | |
| Discard extra dice |
GM: You grab at the knife and get the blade, cutting yourself badly. Give yourself level 2 Harm of 'cut hand'. You do get the knife out of his hand, but can't keep hold of it. It slides away on the floor, away from everyone.
Contested rolls
An NPC will never roll against you, NPCs are not generally built like player characters, and if they are, it's just for GM information and they don't actually roll those stats against players. Instead, the GM will consider those stats when figuring out Effect.
However, sometimes you might have to make a contested roll against another player, either seriously because the game has actually devolved into inter-character conflict or as some trivial contest of strength or some other roleplay. If you want to do that, both of you make your roll like normal, and whoever gets the highest number wins. If you get the same number, you tied that round, and GM may have you roll again, or declare it's a tie. The GM also might consider various aptitudes and allow various ways to increase your roll, or just not allow those and make it a flat roll, especially if it's some sort of joke roleplay scene like wrestling over a remote.