What exactly is the LCS? Starting with Season 3 (We are now on Season 4). League of Legends has hired several teams (through a system of playoffs) and they are now being paid a salary to play games every week for the enjoyment of the crowd. This all builds up to the end of the year when they meet up with the top teams around the world to decide who is the best and take away more then a million dollars.
Why should you watch it? The LCS games are the highest level of play possible for this game. Not only will you see flashy moves, daring escapes, triple/quadra/pentakills but you will also get to see how important objectives are, when you should push towers, and overall how to improve your game to the next level. You'll also learn what champions are currently considered the best by people paid to play the game.
How do I watch? You can catch the LCS live at The Official League of Legends Website or you can visit LoL Event Vod's for replays of every game an hour after its over with. This can also be used to catch up on non LCS tournaments, and past games (Invluding Season 3 world finals) The key games to watch is, LCS Na, LCS EU, and OGN, OGN is the tournament for the Koreans.