Think you have a ant on a sheet of paper now draw two points on the said sheet,and place ant on one point the ant should cover entire distance to reach to the other point however if you fold the sheet so that one point is close to other or mearly touching it the ant doesn't have to travel that long distance which it would had to be traveled when the paper was not folded 

now take the example in space where you replace the ant remember you are dealing with a two dimensional object which turns into a three dimensional object with a worm hole,you are turning a three dimensional object into a four dimensional one 
hope it helps