Plate Tectonics

Earth's crust is made up of tectonic plates. And we're not talking fine china; we're talking gigantic pieces of earth. And these things are moving all of the time! They're floating around on the Earth's mantle, a layer of hot molten rock, which is between the plates and the very hot center of the Earth.
All oceans and continents are on the tectonic plates, so as the plates flow over the molten mantle, islands, oceans, and whole continents move too! Sometimes you can feel the plates when they collide. That's an earthquake! Most of the time we can't really see the plates moving -- they only go about 2 centimeters (less than one inch) every year. It is possible to see a result caused by colliding tectonic plates. If two cars crash, they crumple up. The same thing happens with tectonic plates, but instead of a big repair bill, you get big mountains.
Use some muscle to make mountains!
A big flat table or hard floor

A sheet of newspaper

Lay the newspaper flat on the table or floor.

Put the palms of your hands on the paper about a foot apart.

Now slowly push your hands together while twisting them a bit as you go.

The middle of the paper lifts up off the floor, crumpling as you push. You get mountains just like the Himalayas or the Rockies only, well... smaller.

Nye Labs, http://nyelabs.kcts.org/daily/0702.asp