Doric Order
The earliest Greek temples were built in the Doric style. Doric temples are simple and strong, not fancy like Ionic or Corinthian temples.

In Doric temples, the columns have no base, but just sit right on the floor. At the top of the columns, there's a capital made of a sort of small pillow in stone, and then a square block, under the architrave. On the architrave, there are triglyphs and metopes.

Ionic architecture page
Corinthian architecture page
To find out more about Greek architectural orders, check out these books on Amazon.com or in your library:
Ancient Greek Architects at Work, by J. J. Coulton (1982). An interesting look at how Greek architects worked.
Greek Architecture, by A. W. Lawrence, R. A. Tomlinson (5th edition 1996). Might be a bit out of date.