Welding can be simple yet it can be hard, all depending on what you do with. There are many different welding machines, although I only know how to use the M.I.G. welder, I can still tell you a lot. First of all, what makes a M.I.G. work? Well the M.I.G. welder has a long flexible tube that has a conductive gas and wire (usually copper) running through it. The wire come out from off of a spoil on the inside of the welding machine. The electric current is ran through the wire from the machine and into the metal being worked with. Most welding machines have a chart that shows you what voltage to use with what thickness. How do you make a basic weld? It's simple, think of frosting a cake (for those of you who have). The concept is similar, you take the gun and make a line in a swirling motion, now you can weld most things together with this basic technique, but not all. Let's talk grinders and sanders. When working with belt sanders always remember to never put a sharp edge or an edge not smoothed after being cut with a torch against it. With angle grinders check your workspace completely before running and keep your piece in place with either a magnet or clamp (there are other ways), because if your piece is not held in place somehow it will move and possibly get ruined.
I hope this information helps.