Trying to understand subroutines

[Catone]

If anything, you would do a bit check for a direct jump if true, to your new code, then another check and jump back to the original code that opens the world map, the other option would be to jump like that to your code, then follow your code (still in 3F/) with the code that opens the world map, following that with an FE to end the code without ever returning to your start point.

What is the line that Cyan says when you talk to him? I'll look at it and see if I can provide a more clear answer.