Branching lets you fork your journey at any turn to explore a different path without losing the original.
You're redirected to the new journey, which contains every turn up to the branch point. From there, you play forward with new choices. The original journey stays exactly as it was.
Branches are full, independent journeys. They show up in your journey list alongside everything else. The original and the branch don't affect each other: advancing one doesn't change the other.
Creating the branch itself is free. Only new turns you play after the branch point cost credits, same as any other turn.