The merry-go-round is a very simple design.  For the most part they have a circular piece of metal or wood suspended above the ground and anchored at the center.  The anchor allows the merry-go-round to freely move in a circle.  It also contains bars for people to hold on to.  Normally kids will get on and one will start pushing it in one direction until it reaches a desired speed and that kid will jump on.

Besides that type of ‘playground merry-go-round’ there is also a carousel.  These are mostly seen at amusement parks.  For the most part they have the same simple design as a merry-go-round.  It is a circular piece suspended above the ground and anchored at the center.  A carousel doesn’t have bars to hold on to but rather poles from the ceiling to the floor with some type of fake animal for you to sit on as the ride goes in a circle.  Also this type of ride is motorized, so no pushing is involved, besides the start button of course.