From http://www.solarviews.com/eng/earthint.htm
The Earth as a planet is fairly modest-sized. It is the largest of the 4 terrestrial planets (what are the other 3 terrestrial planets??). It has an atmosphere that covers the solid surface. Its composition is primarily iron and rock, so it has metals and heavy elements. Its surface temperature and pressure is such that liquid water can exist on its surface, and it is "just right" for conditions for life (Goldilocks Effect).
Here are some spacecraft images as well as more true color images of our home planet.
Hurricane Isabel as seen from space!
Since we cannot directly sample the deep interior of the Earth, we must resort to indirect methods for studying the Earth's interior. One of these is the study of earthquakes, which generate seismic waves that travel through the Earth's interior. Some of these waves travel along the Earth's surface, while other waves travel through the deep interior of the planet. The Earth's response to these waves is indicative of its composition.
We now know that the Earth's interior is composed of several different layers, as shown below. The crust is solid, and is made of rock (basalts under the oceans, granite under the continents). The mantle is solid, but may be a slowly moving fluid (like cold honey) at great depths. We can occasionally sample the mantle when volcanoes erupt. The core is the most dense part, containing iron and other metals.
From http://www.solarviews.com/eng/earthint.htm
The Earth behaves as if it has a large bar magnet running down the middle of it. The magnetic field comes from the moving liquid metal in the Earth's core, which generates a current. The Earth's magnetic field creates a region around the Earth known as the magnetosphere, within which charged particles will be trapped. The Sun is releasing charged particles all the time; some of them become trapped in the Earth's magnetosphere and cause the aurora (Northern and Southern Lights).
The Earth's crust is made of several different kinds of rock:
The Earth's crust is divided into roughly 12 plates that fit together like pieces of a jigsaw puzzle, and that move slowly relative to one another. At one time, all of the land masses were closer together (see the progression of the continental drift here).
There are several different ways in which the plates can interact with one another (pictures are from http://pubs.usgs.gov/publications/text/dynamic.html:
The mechanism for plate tectonics is a process known as convection, which involves the rising of warm material from deeper in the mantle, the cooling as it reaches the surface, and the subsequent sinking of material. This is the same process you witness when you have a pot of water boiling on a stove. The crustal plates are floating on the mantle. Thus, they move around slightly as these "bubbles" of material rise and sink beneath them.