Calling
The Calling tab is where you can view your call history, and where you can pull active calls from another device
Dialpad
The Dialpad is where you can enter numbers to place outbound calls.
Contacts
The Contacts tab is where you can manage contacts and place outbound calls to those contacts
Voicemail
The Voicemail tab is where you can listen to and delete all your voicemails in a visual manner.
Search
The Search tab is where you can search for extensions (users & services) in your organization
Profile & Preferences
The Profile & Preferences menu is where you can access Do Not Disturb, Settings, and other app functions