There are a lot of resources available on the web. One great site to get a lot of information and links to other sites is:
http://www.airfieldmodels.com

A gas engine burns regular gas along with oil, and has an ignition.
A glow engine uses a ntiro/alcohol oil mix, uses a glow plug no ignition.
A brushless electric is an electric motor that has rotating magnets fixed coils and does not have the normal brush setup as common electric motors have.