I tried to find you a decent video, but couldn't find one. This is hard to explain, but I'll try.
Ribbon (or stringing) technique is basically picking up a string of gel, rather than a blog, and guiding the string back and forth over the nail. This can be used to create an apex or to fill in dips. This is related to the "T" or cross method, where you would string the gel in a t section on the nail to help create the apex.
Hope this helps.