You help another PC on a roll. State how & why, then roll 1d and share the risk. Include your roll result with theirs for the final outcome - then each narrate your contribution, using your result and bonds as a guide.
You can assist when another PC’s actions prompts an impact move. You make a 1d defense roll for them.
When you share the risk, you open yourself up to the consequences, which can prompt a more powerful or additional impact move, or the GM can take suspense instead.
When 3+ PCs work together, the GM picks who rolls the action - sometimes the most skilled, sometimes the least. The other PCs assist.
When a previous action makes a follow-up more effective, you assist without risk. You roll 1d as a normal assist, but don’t share the risk.
When an assist or setup comes from the world, like an NPC or the environment, the GM rolls 1d to represent it.