How do I find displacement

The displacement is just the distance between the starting point and the
ending point, and you don't care about the route taken or the actual distance
covered along the way.

This can bite you sometimes.  For example, some day you'll be given the
diameter of a circle, and you'll be asked for the displacement of an ant that
walks around the circle 17 times and finally stops at the same place it
started from.  You might go to work calculating the circumference of the
circle and multiplying it by 17.  But if you think about it first, you realize that
if the ant ends up at the place he started from, then his displacement is zero.