When a vehicle is driven in a straight line, the wheels on the left side and right side of the vehicle should be parallel with each other. If one wheel is slightly off, the vehicle may want to pull, or drift, to one side. If the vehicle drifts, then a wheel alignment is needed to return the wheels to the correct position.
Most automotive shops, especially those that specialize in tire repair, have wheel alignment equipment that checks a vehicle's suspension and steering angles to make sure they are properly adjusted. If the suspension and steering components are even slightly out of adjustment, it cause tire wear.
It is important to have a wheel alignment performed if needed. It will cut down on tire wear and prevent added cost of buying tires more frequently. Some manufacturers, as part of their factory warranty, have a limited warranty on wheel alignments.