Its not a good idea buying a motor without any specifications like this - you have no way of complaining if its the wrong motor....
Usually stepper motors come with these specifications as a minimum:
max current for one winding, winding resistance (or voltage at rated current), winding inductance, holding torque at rated current, number of steps, moment-of-inertia of rotor.
We crucially need to know the first two, current + resistance (too much current can damage the motor thermally or magnetically). winding voltage and resistance are related to current so either will do. Resistance is easy to measure, rated current you will have to guess.