I don't know of any specific sites or books I could recommend on 3D modeling techniques/terms, but if you Google something like this:
http://www.google.com#q=3d+modeling+basics
you'll get at least a few sites that cover the basics. Not ideal, but hopefully someone else has a specific site they could recommend.
The next best thing is to start with simple tutorials, and, when you're thrown a curve, feel free to ask questions. The users on this forum are very friendly and usually happy to help.
For your example, "you need to cap the end of the cylinder":
If you think of a cylinder as a shape with a top, a bottom, and some number of sides (like a cylindrical umbrella stand, perhaps). the top and bottom would be the "caps". So to "cap" an end might mean to add a surface/polygon to the top or bottom --- this would imply that our cylinder did not have a surface on the top and/or bottom, that it is open-ended on one or both sides.
That being said, it could refer to texturing or other techniques, but for basic modeling, that's what "capping" a cylinder usually means.
Good luck,
Dennis