So, just to clear one thing up, does your cs go up when you get the last-hit?

Also can you see your CS in game?

-Kjelsauron

Yes, CS is how many monsters you got the killing blow on. And yes, you can see it in game. Press tab and it will show the scoreboard for everyone in the game. (and yours only shows next to your kills/deaths/assists)

Trigbomb aced it but just to kinda shed some light... If you are jungle you should have moderate CS but for someone like solo top or ADC your CS should be pritty high and for support you should have the least amount of CS in the game. CS is a way to basically get a ton of coin and XP fast without having to coordinate ganks so CS is very important in the game.

To add to Trigbomb's post,

CS is considered highly important as 1 champion kill (without bounty) is typically worth somewhere around 20-30 CS (depending on which creeps are killed). So even if you aren't killing your enemy, if you are farming CS better you are winning the lane.

Not all creeps are equal. Siege minions are worth more than melee, melee are worth more than range minions. All jungle minions start with relatively low gold worth, but they become extremely valuable around the middle of the game where the main minion in each camp can be worth 50+ gold.