An extension's availability will be reflected by the color in the upper left hand corner of the Live Extension box.  

Green - if the extension is available, with no pending calls 

Yellow - if the extension has a call ringing inbound, also if the extension is making an outbound call that has not connected. 

Red - if the extension is currently on a call 

By default, all online extensions will display. You may chose to view extensions that are offline with the check box displayed below- 

You may also use the search bar above to filter the extensions in the Live Extension view. You may search by an extension's name or number. 
You can sort the display either by extension number, or alphabetically by first name or last name.

You can favorite an extension by selecting the star next to the extension number. Any extensions you favorite will display under the "Favorites" filter, and at the top of the list under "Extensions" filter, and also at the top of the list under your "Outbound" filter. 

The Info button (white "i" in black circle), will display the extensions phone number as well as other user information, such as email address.