A +1 close-up lens is a "filter" of clear glass with a focal length of 1 meter. So if your camera is focussed at infinity, the combined lens/CU+1 system is focussed at 1 meter. There are cheap ones, and anastigmatic (?) ones.
Extension tubes move the whole lens away from the film, same as happens when you turn the focus ring to focus closer. A good choise is one which starts about where the lens stops - which of course depends on the focal length of the lens. There are tables to be found, or you can try to calculate it yourself from the basic "thin lens" equations.