map is a transforming filter: it takes the right side (after the code block), transforms it according to the code block, and spits the transformed pieces out the other side. Think of it like an assembly line:

• a bin of widgets is dumped into the hopper at the beginning of the line
• A whatzit is added to the widget to make a whatever
• a bin of whatevers is left at the end of the line.

Does that help explain it at all?