When an engine is really old or has been sitting unused for a long time the internal components are going to be less likely get going. You can liken it to Newton's first law where he said that an object at rest tends to stay at rest. This just means the engine will need a little coaxing.
Since the engine hasn't had any oil running through it in a while it will need to be lubricated. You can do this using a product called Marvel Mystery Oil to lubricate the cylinders, pistons and rings. You can do this by taking out the spark plugs and pouring a small amount of oil directly into the cylinders. The plugs will probably need to be replaced anyway.
There are two different ways to get the engine to turn over at this point. In some cars you may be able to turn the engine over using a socket wrench on the crankshaft nut or you could hook up a battery to the ignition. Any oil that's in the cylinders will come out when you do this. If the engine turns over after you crank it then it may start up once the spark plugs are replaced. If your engine has a carburetor some people recommend spraying starting fluid into the carburetor to help get the engine started.
Getting the engine to turnover is a good sign, and if you've already corrected some other problem areas then the above suggestion may be all you need. But even if everything is working properly with the engine there still are several other factors that you need to inspect before you can get the engine running for good.