mwin, I see you are brand-spankin' new to the forum, so perhaps you didn't realize that we need more information before we can even start to assess your problem. Here are some of the questions that we need answers to:

1 What engine is in your tractor?
2. How long has it been since you last ran it?
3. Did you leave fuel in the tank and/or carburetor over winter?
4. Have you checked the obvious: fresh fuel in tank? gas shutoff valve open? any loose wires? is there spark at the plug? is the air filter clean? is the spark plug clean and properly gapped?
5. When it last ran, did it run okay?
6. When it cranks, does it seem to be at a normal crank speed, or does it just turn over s-l-o-w-l-y?

From what little you told us, my guess would be that you left gasoline in the carburetor over winter, and your carburetor is gummed up.

One piece of advice: DO NOT start turning those adjustment screws on the carburetor. Carburetors do not un-adjust themselves.