Used to address a familiar person during a conversation, an informal form of you
Depending on the nature of the conversation with the person you are addressing it can be used for dramatic effect.
The equivalent of using the word Yo
It can also be used to express disgust or disaproval with a person, comment or event
Chal! let me tell you what happened last night (dramatic expression)
Chal please! (disgust)
Chal! (disgust and dramatic expression)
I talked to her last night chal (addressing a friend or familiar)