The fourth finger of the left hand is tradtionally the 'ring finger' this the finger next to the pinkie on the left hand.
Anyway, the ring finger is the finger between your pinkie and middle...
According to the Oxford English Dictionary, it's derived from the obsolete adjective "pink" meaning small, which goes back to the 16th century. It is not in any way related or connected to the color...
Because that is the finger that engagement and wedding rings are traditionally worn on. Rings tend to get in the way if on the Pointer and the Little fingers. For most people a ring on the Ring...