how to Implement an java application?

Hi, every body!
I have to implement a chat software:
- have server and client
- can register, login..
- server manages status and imformations of clients...

I think I have use multithread and socket, RMI in java. But I don't know how to implement it. Can you help me?
Thanks alot! ( Sorry for gramar's error 😀 )
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