Take the #1 side rocker cover off, turn over the engine with a breaker bar on the nut of the damper (tightening) until the #1 intake opens and closes and the timing mark comes up to the pointer. If you have a manual it should show you where to aim the rotor it’s normally towards the carb but to some it doesn’t matter. Insert the distributor and seat it on the flange. Set the cap on in its notch and the post the rotor is aiming at is your #1. The plug wires can now go on the cap in the correct firing order follow the direction the rotor was turning. If the spark plugs are not in mark the wires with the number they should go to. This should get you close enough to start and run the engine, minor adjustment but slightly turning the distributor to bring in the timing marks to specs. I’ve used this on hundreds of engine and rarely had to move one unless the vacuum can hits the intake manifold which I have learned to have enough room in either direction to adjust the timing + or - 15-20*.
If better/easier descriptions are posted I will delete this one.