The situation is still not clear. The steering wheels pull by itself or not? Answer in yes or no.
If not, Then its just the steering position adjustment needed. Open the steering cover (horn part). Bring the steering wheel at a position where the car go straight. Open the steering nut, pull out the steering and put it back again in the center position. Or just go to mechanic and tell him to center the steering wheel.
If yes, you need alignment, or check your wheels/tires and it will be done by an alignment guy.
Please read the above reply. There can be a simpler problem there.
One should start by ruling out problems and proceed with the smaller first.
Remember, your 50% job is done if you successfully diagnose the problem. Or you will be wasting money on parts and filling the mechanics pockets...