There are two beasts described in Revelation 13; the First Beast arises out of the sea, having seven heads and 10 horns. The Second (Lamb-like) Beast arises out of the earth, having the appearance of a lamb while speaking like a dragon. This Beast exercises authority on behalf of the first beast, causing the Earth-dwellers to make an image of the First Beast, and worship him. It is able to give life to this image so that it could speak and kill anyone who doesn't worship the First Beast. This Beast is later called “The False Prophet” (Rev. 16:13; Rev. 19:20; Rev. 20:10) and together with the Dragon and the First Beast forms the unholy trinity.
Personally, I'm not a huge fan of the book of Revelations - but that's just me...