How to use add selection tool

I can't find any instructions anywhere on how to use add selection tool in Pattern Editor. Can someone advise?

If you use the rectangle selection tool to select an area and then want to add another area to what is selected, you can use the add section tool. Or if you just want to keep selecting areas without the previous selections unselecting, use the add selection tool.

Can you use desinger to draw a object and copy or export as a jpeg or other type of fife or print out as the file the size you created Thanks Bert