When you hear the word play in slang, it usually means one of two things. First, it could be referring to sex. This is probably the most common use of the word play in slang. It's often used as a verb, as in I'm going to go out and play tonight. This simply means that the person is planning on going out and having sex with someone.
The other common use of the word play in slang is to refer to a game or competition. This is usually used in a more general sense, as in I'm going to go out and play some basketball. In this case, play simply means to engage in a physical activity for fun or recreation.