First you must find how a stepper motor work and for that i have a video for you.
You whill find all you need about stepper motor.
Step 1: Now ...How to Do This..
Now take Meter + and connects to a wire of the stepper motor now whit the -- coneect to the other 3 wires stop when you have a resistance you have the first coil ,now check the two wire who remained you must have the same resistance ,now you have 2 colis .
Here you can see that the first two random wires measured open, and
the second two measured 1.8 ohms. This is a typical large-ish 2 phase stepper.