Forging is a technique in which you use a hammer to flatten, shape, and texture metal. Any amount of hammering will gradually harden your piece of metal more and more. So for example, if you're using soft sterling silver wire, you may want to twist and bend it to a jewelry shape. Well, you want it to keep that shape, and not stay bendable. You'll finish it by hitting it with your hammer to harden it, and hitting it more if you'd like to give it a little texture while you're at it. For silver, copper, and brass, you don't use heat when you're forging. Hitting it with a torch is actually called annealing, and that will end up softening it. If you want to use a torch to add color to a piece of copper, for example, you'll then want to forge it to get it hard again.
And that concludes our mini-tutorial for today. Use the word forge when you're hardening and bending metal. Don't use it just to sound like a macho metalsmith. I've seen descriptions of jewelry on the internet that use "hand-forged", and yet it doesn't appear that a hammer has hit the piece at all. And besides that -- forging shouldn't be so macho, bang, bang, bang. You need to gently hammer and finesse the piece. Banging the heck out of it will not give you an attractive look.
Here are some pieces that I forged: