The Calling tab is where you can view your call history, and where you can pull active calls from another device

 

The Dialpad is where you can enter numbers to place outbound calls.

 

The Contacts tab is where you can manage contacts and place outbound calls to those contacts

 

The Voicemail tab is where you can listen to and delete all your voicemails in a visual manner. 

 

The Search tab is where you can search for extensions (users & services) in your organization

 

 

The Profile & Preferences menu is where you can access Do Not Disturb, Settings, and other app functions