1) What are these things: LCS, ECS, OW, 4-pool stand :
They are acronyms of the tournaments that are hosted for a particular game.
LCS = Legends Championship Series (League of Legends) Wikipedia Info
ECS = E-Sports Championship Series (Counter-strike)
Mainly they are for high skill players (commonly streamers and other professional teams) who dedicate to a particular game and compete for cash prizes.
2)Is there something about eSports that connects these games? League of Legends, Counter Strike GO, DOTA 2, Starcraft 2, Call of Duty, Heroes of the Storm, Hearthstone and World of Tanks.
They all have large communities who play these games, and the developers of the games often either endorse Competitive play, or even host the tournaments with the players often being invited from around the world to play. They often involve 2 teams squaring off in PVP combat (notable exception is Hearthstone which is a PVP card game). Many of Blizzard's games are PVP based in nature or allow for a competitive scene. League of Legends, Smite, Counter-strike, DOTA 2 are all popular games, and have pretty high skill requirements to become "pro" and as such the best players are often very well known within the respective gaming communities, and people love to watch them play.
Hope this gives a very brief overview to the subject, and is by no means exhaustive but should give you an idea now.