How do I link nodes?

This is probably a very simple question. I am trying to do the normal database relationship between types, one-to-one, one-to-many, many-to-many.

For instance, let's say I create a new type "Carnival." And I have an existing type "Rides." When I create a new carnival, I want a drop down list of the existing rides. When I click on the list of rides, I want to see which carnival to go to. I guess this case is actually many-to-many. Basically, I want custom types to be able to be added as elements of other custom types.