Or start here in the menu that says Get Screen Name and work Left to Right.
This is an iChat 4 how to but broadly can be transferred to later versions.
In summary it is
Get a Screen Name
Enter that in iChat
Click Buddies in Buddy List or their Video or Audio icon to chats.
I may receive some form of compensation, financial or otherwise, from my recommendation or link
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously