NEWBIE!! I am looking to create a circuit that allows a motor to go in one direction for a distance then reverse for a distance then reverse . . . an so one. The application is moving a rack and pinion to motivate a slotted board back and forth over another slotted board.
I have the schematic from another post but I don't understand how it works.
any help is welcome!

 

Post the schematic you have. That could be a good starting point.

 

you could just use micro switches at each end to flip flop the voltage across it. no circuit just wires and switches.

 

or ...... You could use a low speed motor with a crank and connecting rod. (Windshield wiper motor comes to mind.)