The Talk window will open.
Press the Create chat room button below the Talk main area. Enter a name for your topic. If you wish to create a persistent room uncheck the Temporary room box and click the Create.
Select the user you wish to invite to your discussion and click the button to the right. Or simply drag and drop it to the Talk main area. The invitation will be sent to the selected user.
To facilitate the search of the necessary user you can enable the filter clicking the corresponding option above the contact list.
The same way you may add as many members of the chat room as you wish.