FollowPath constraint binds the owner on a spline path, and moves owner based on an offset value. The constraint can not only affect the owner's position, but also set the rotation of owner based on the spline's setting.
When offset = 0, owner at the start; When offset = 1, owner at the end of spline.
(Check Spline Editor manual for instructions on how to make spline)
Check the preview image below:
Here we explain each options in the FollowPath editor;