Depends on the context but normally it means that you are not good at something. You are bad, awful... =p Person 1: Let's play... Person 2 : Let me warn you, I suck at football.

Person A: It sucks. Person B: What sucks? A: The leech sucks. B: Oh, right! Sucks what? A: Sucks blood. From my arm. B: Well, get rid of it then. A: Oh no, it has left a big mark! B: Oh, that sucks!

suck意思是 吸 。譬如喝蒙牛优酸乳，你就要用吸管吸。 当然，吸这个动作不仅能吸吸管，更能吸其他的东西，部位，器官，譬如说 JJ（cock）。所以，suck有blow job的意思。 所以他也有恶心，X,烂的意思。

It is related to oral sex. Should not be used among intellectuals.