Wow you got a lot to learn. use the search bar, or this:

shapefit.com/

One exercise, one set, 15 reps, same weight for one year? No wonder you're not gaining any weight. Get a proper routine going and gradually increase the weight.

And even if you had a decent routine, you're not gonna gain anything if you're not eating. You need to eat. Lots.

Don't give up, you haven't even tried yet. You have much to learn. Far too much to put into a forum post. Do some reading, lots of it. Here's some help.

Let me google that for you
Let me google that for you
Let me google that for you

The Bodybuilding.com forums are good too, but be wary of the articles.

So I've been lifting weights for the past year and seen no improvement at all. Still the same stick I've always been:P Maybe I just don't build muscle mass? My workout involves lifting 2 15 pound dumbbells 15 times, 3 times a day. I've done that for a year with nothing! Help!

You need to learn to use google my friend :p I see two problems with what you are doing. First off it's great that you started off with 15 pound dumbbells but after awhile you need to increase the weight of them. Every month you should have increased the weight by 5-10 pounds. Sticking with the same weight gets you no where besides being REALLY good at lifting 15 pounds. Second you need to change your diet to a lot more meat. Exercising and trying to build muscle does nothing when your scarfing down Doritos, or Coke, or whatever unhealthy thing comes to mind.

Yeah don't give up. It's more than just lifting some weight up and down 45 times. When trying to build muscle, everything has to be done properly or you won't get good gains. This includes your diet, workout, what's done in your resting periods, how much sleep you're getting. It be a lot to explain here so just do what everyone else says and google it. Read from more than one source so you can figure out what info actually works. Don't go blasting your money on all of the books that claim to have the secret too! Expect to spend a lot of time researching too.