You've found a good place right here for advice and tips. There are a couple good books you can find at your LHS or possibly at www.rcstore.com

Gas engines run of gasoline like your car and use a spark plug...

Glow engines run off of glow fuel and use a glow plug, sort of like a diesel engine.

All engines have bearings...There are bushing type and ball bearing. Ball bearing engines tend to have more power and runs moother. They are a little more expensive too, but are usually of a higher quality.

Bushing type engines are usually just standard sport engines witohut a lot of power. They are cheap and will last for a very long time if oiled properly.

There are a couple types of engines including ringed, ABC, ABN, and AAC. All gas engines and car engines are ringed. A small number of glow engines still use rings. ABC are VERY popular for glow...

Get an engine recommended by the manufacturer of your airplane. If they recommend a .40, stay within the .40-.50 range.

Try this place-

http://www.easyrc.com/engines/index.html

Read all you can and also check out the links from that page to books and other references.