Middle Screen
The green area is Work Area. Here do you work with pen tool, selection tool, circle/rectangle tool and a lot of more different tools.
The red Area is just an area that fill the space with nothing. It's not useable.
Blue Area is the minimap. Every time you draw a block in Work Area and this block have a minimap color. That color is going to be seen inside this minimap window.
You can use your mouse cursor and click on the minimap. This will automatic move to the new position from minimap, inside Work Area.