It is slang,but notice that it is not a very proper expression to use, only informally and with close friends. It is used to express resentment, dislike or feelings of disgust about something or a siutation.

It can mean that's not good, or be used like "thats not fun". If someone said " I have to take out the garbage" you might reply with "that sucks" because you don't like taking out the garbage and you are relating to the other person.

It means "that is awful!" 那是可怕的

does she mean "that's sucks" or "that sucks"?!.

意思就是逊毙了