DAVID: you have to be careful. You're very likely going to make yourself very ill with whatever concoction you have in that jar. It is definately not beer. It will probably have some alcohol in it, but you'd never catch any of us trying to drink what you have made.
True: making beer requires only water, barley and yeast.
False: throwing water, raw barley, and yeast into a jar with some table sugar will make beer.
The barley has to go through some processing to make it ready for beer making. I am SURE your barley has not gone through this process.
Then, everything has to be sanitized reall REALLY well.
Then you cook everything together.
Then you put it in a jar with yeast.
Oh... and I would suggest waiting until you are a little older. I don't know how old you are, but I SERIOUSLY doubt that you're 25 like your user profile suggests.
No one can stop you from trying to make beer, even if you are only 12, but you should listen to everyone here and really read some more on the subject (there are many resources on the internet) before you try to drink anything you are making.