I suggest you google for 'stepper motor tutorial', there's plenty of help out there.
As your motor only has four wires it's going to be a bipolar motor, so you should have two completely seperate windings, easily indentified with a meter.
Once you've found the two windings, use a battery and a couple of pieces of wire to find the step sequence you need.
For a start, label the wires, 1-2 for one winding, and 3-4 for the other. Apply the battery, positive to 1 and negative to 2, and see which way it moves, then apply positive to 3 and negative to 4, and see if it moves the same way - you now know the polarity of the coils.