What is fiberglass, what can you do with it, and how do you use it?
Fiberglass is a composite of glass fibers, either loose or woven, covered in resin, and used for industrial applications requiring high strength-to-weight ratios.  The uses of fiberglass are virtually limitless, but typically found in boats or cars requiring sturdy shells with little weight, and also in insulation.  The actual process of using fiberglass is similar to that of papier-mâché, where as the liquid resin is applied over the woven fabric.  Once dry, it can be sanded smooth and painted.

The general process
This is how the initial shape is created, and how the fiberglass is actually applied.  I use several different methods of applying fiberglass though, each beneficial in its own way.  These methods can be combined or modified as needed, but generally work well for the swords and armor I've made.

Materials                                What to get, where to get it, and how much it costs

Fiberglass over foam               Great for large bulky objects that need to be light weight such as armor and massive swords

Fiberglass over steel                Great for thin sturdy weapons and blades

Sculpy/Putty sculpting              Great for ornate details and engravings