Overview
The Caro Kann Defense is one of the widely known openings for black. The main goal of the opening is to:
Put pressure on white's bid for the center
Use the light-squared bishop to block white's development
Use the dark-squared bishop to launch on attack on the d-pawn with the f-pawn if white chooses to play the Advance Variation
Launch a deadly attack on white's kingside later on in the game (similar to the way it is done in the King's Indian Defense)
Use the queenside to play around the center and attack white, majority of whose pieces are probably higher up the ranks, leaving the king vulnerable
If played correctly by both sides, the Caro Kann usually leads to a draw. However, due to the high amounts of tension in the position, any slip-up is enormously costly, and leads to a huge advantage for the other side. So, I would not recommend playing this opening in bullet or blitz games (trust me, I've tried).