How to create a chat webapp on the webpage

Dear sir,

I am creating a website and there i am adding a live personal chat page like a facebook
pls help me or can you provide me the code?

And when the user is login they two user's are go to chat on my site
like a : -

example:-

"User1(Rahul): Hello.
 User2(Vishal): How are you?"

like this. pls help me.