Toe is the angle that directly effects whether the steering wheel is going to be centered or not.  Toe is pretty amazing in how it works and effects vehicle driveability.  This is the angle that the tires point when looked at from straight ahead. Think of it as feet; some people's feet point inward when standing, some are straight ahead, and some point outward.  The strange thing about toe.. it equals out on each side when the vehicle is moving down the road. They will pull themselves to the point of being equal. 

If the left wheel is toe out -3degrees, and the right is toe in +1degrees, the steering wheel is going to be off to the right by 2 degrees! So essentially as the vehicle travels down the road, the steering wheel will be "turned" slightly right to make both toe measurements equal the same measurement which is -1 degrees tow out.