1.In YateClient main window, go to Yate->Add account wizard:
2.Choose IM (Instant Messaging) account, like in the screen below:
3.By default, the next screen will have the "Advanced options" hidden and it will confirm that jabber protocol is used. You will then type the domain name :
For example, you can use your firstname.lastname@example.org, once you have it registered at http://register.jabber.org/.
You can also choose to register a new account, but take into consideration that this option will only work on the jabber servers that actually allow this.
After you added this account in YateClient, you can always log onto it from now on by using Settings->Accounts in the main menu.
Screenshots are from YateClient version 4.0.