These filters are called "close up filters", see Google for more reading material, including
Close Up Filters (Macro-Photography.org)
Basically, these are a strong magnifying glass mounted in front of the lens, so the lens can focus closer. The +1, +2, +3 nomenclature is diopters, and the reciprocal is their focus distance. +2 means 1/2 meter. That's the focus of the filter alone, the lens combination will be that if the lens is focused at infinity.. (EDIT to correct error).
It is difficult for these to keep the frame edges sharp, and best results will be when stopping down considerably, like f/11.
The best of these filters have two glass elements, which reduces purple fringing around edges of colors.
The Canon 500D close up filter is considered one of the best - yes, it even works on Nikon lenses too
I don't think the 500D has a 67mm version however. Nikon used to make two element closeups, but don't now. Macro lenses are substantially better and more versatile, if you pay the price.