I just bought it for $10 and the chain and gears are rusted. When I ride it the chain seems to slip. I barely have any money, do I just need to lube the chain? It's a 5 speed.
Get another chain and a chain breaker at Walmart. WD-40 is the worse thing you can use on a chain it's a degreaser and will remove any lube that is in the chain. You can use a chain saw oil that is made for the chain or get regular chain lube from a bike shop. Walmart started selling bicycle chain oil but I forgot what it was, it's a good brand. It won't hurt to try about any oil you have at this point.
Loosen the nuts on the rear tire and pull it back more, therefore making the chain tighter, tighten the nuts with the tire further back, you're done.
If the chain is rusty it wouldn't hurt to use WD40. Also, check the masterlink on the chain, if one of the links is broke on one side its the masterlink, you can pick up a new one at a biking store for 40 cents to a dollar.
Well if the chain is rusty then DO NOT add WD40 to it that will make it worse! If you have some heavy motor oil anywhere then that would be better than anything else. No real good way to help a rusty chain and WD40 will only invite rust and should only be used to degrease, not lube! Pull that wheel back and retighten it , that will keep it cheap for you! Edit: Bob is correct, cant move that wheel back any it is a 5 speed....I knew that!! duhhh!