Creating a conference room is pretty straightforward. Choose Actions and then Create a conference room....

The Create a Conference Room window appears. Type the address of the conference service of your server in the Service address field. (Sometimes it's also called groupchat or MUC.) Type the desired name for the conference room in the Room name field. If the name has already been taken, try another name.

Press OK to create the conference room. You will automatically join the conference.

As you have created the conference room, you are the administrator of that conference room. This gives you some extra options. You can, for example, change the subject of the conference room. To do this, choose Actions and then Change the Conference Room Subject.... There are also some more advanced options. In the Actions menu, choose Configure this Conference Room... to access the advanced options.

If the conference already exists, you can join it. To do that, choose Actions, Join a Conference Room.... You'll now see a list of all the conference rooms on your Jabber server. You can join the conference by left-clicking on the name of the conference room.

If the conference room is on another Jabber server, press the button Other Service.... Then type the full name of the conference service of the other Jabber server. In many cases this name resemble conference.jabber.org. After you confirmed your choice by pressing OK, you'll see a list of all the groupchats on the other server.

You can invite contacts from you contact list to a conference. Your contacts still have to accept your invitation before they will join the conference.

This process is the easiest if you are already in a conference room. If that is the case, right-click a contact in your contact list. Then choose Invite to conference room. Pick the desired conference room from the list.

If the conference room doesn't exist, you'll first have to create one. You can create a room and invite someone in one step. Right-click a contact and choose Invite to conference room. Now choose Create a new room. You will now see a dialog window to create the conference room. After the room has been created, your contact is invited to the conference.

You can change your name when you are in a conference room. To do this, choose Actions, Change my Name.... Type your new name in the Change my Name window. After you have confirmed your new name, all your contacts in the conference room will see your new name.