Well, it depends what you are trying to do but generally you will group the entire rotor into one group. Then you can select the group and then go up to "Rotate" under the Edit menu. The angle you need to rotate it for each step is going to depend on a number of things (number of poles, number of slots, speed, etc.) but basically you want to make sure you have enough resolution. That's how you actually get the motion. From there, you can do a number of things. If you are looking for cogging torque, you can select the entire rotor group in the magnetics output screen and get the torque at each angle you move through. Plot it out and you get cogging torque. The back-emf takes a little more work. If you go to circuit properties in the magnetics output screen, one of the outputs is flux linkage. Back-emf is just the derivative of flux linkage with respect to time, so if you get the flux linkage at each angle, then you can approximate the back-emf if you relate each angle to time (based on the speed of the rotor).
You can do this with or without Lua scripts. There are plenty of examples on the FEMM website that you can use to modify Lua scripts.