Web based chatting application [on hold]

Hi all I would like to create my own php , javascript based chatting system which is something like internal use limited for 10 people right. The system has predefined credentials for each users 1 . user login 2 . user dashboard 3 . can see other users 4 . click on any user 5 . start chatting 6 . submit 7 . the submit chat will send to the particular person

basically backend by php server side query mysql , frontend javascript

please give me suggestions ideas for improve this and my question is let's say I pre configured 10 users 1 to 10 user 1 want to chat user 2 user 2 want to chat user 1

this would be normal but let's say user 3 want to chat 1 5 want to chat 1 1 want to chat 2

how to pass their message to accurate users ?