How to fix the distributor?

I have a 1968 ford f100 pick up and the distributor isn't working. How do I fix it?

Verify spark at the plug. Ohm check the wires inspect the cap and rotor, put a set of points and condenser in it, perhaps a new breaker plate. An open in the coil wire makes a short day of it.
You should, while cranking, have power on the + side of the coil and a flashing test light on the distributor side of the coil. Showing the points are opening and closing.
The breaker plate locates the points and controls their relationship to the distributor cam. You could still get a new one. I have seen them on e-bay.
trucks use a different height cap and rotor. Make certain you have both for a pickup truck.
The ignition coil needs a 12v circuit for starting, and a resistor circuit for running, make sure you don't have 12v all the time or an open resistor wire circuit. Having a "hot coil" makes a bad one out of it.
those are some basic guesses for you.
Otherwise you need to provide something to go on.

Distributors are pretty basic. Replace the points and set them to the right gap. If the distributor doesn't turn when you crank the engine, you have more serious problem such as a broken timing chain.