It has a 19mm or 3/4 nut that locks the hex screw. Clockwise loosens the wheel. Counter Clockwise tightens. I'm glad to know that it is more likely that nobody looking for a fast buck worked on your car lately. Your problem is more likely the part that you are describing. However, if your steering wheel is tight as it should be, then the car is going to go only in the direction that you steer it. If it does something else, then you are out of alignment and possibly have damaged components that probably need to be checked out at an alignment shop that you can fairly and reasonably and hopefully trust will a good job for you.

BenzDiesel