This article is from the Radio Control (R/C) Flying FAQ, by Shamim Mohamed firstname.lastname@example.org with numerous contributions by others.
Gliders are usually launched by a "hi-start"---a section of rubber with
about 500' of line. It is hooked to the plane and pulled back---the
rubber then pulls it up kite-like. (It is NOT like a catapult launch!).
Launches of heights up to 500' can be obtained on a good day. The launching
procedure is simple---keep the elevator neutral (for now) and keep it
flying straight. At the top the glider will just fly off the line. A small
engine can also be used but it creates a lot of drag which is very
detrimental to gliding performance. Hi-starts range from around $20 for
light-weight models to $100 for heavy-duty ones.
Winches are also used---it's very similar to a high-start except that you
(the pilot) always have control over the line tension so you can usually
get better launches. It does take more skill, though; as a beginner you
don't need to worry about winches just yet.
Flying at the slope you just chuck the plane into the wind---that's it!