How to add a layout to my youtube profile ?
You can only add an actual layout if you are YouTube partner. Otherwise, you can only edit the look of your profile ie) colors and background image.
The difference between layouts and the look are the features. Layouts allow you to add more links (mostly to outside websites) and to create overlays onto the wrappers.
Changing the look, again, is just changing the colors of your page.
when you see the image you want as your background right click go 2 properties go to te URL and C+P it to Youtube