This is very simple to make an outbound call. To call out from inside the 2ndLine app:
Tap the phone dialer icon on the top right of the main screen to bring up the dialer.
Select which destination country you would like to make the call to.
Type in the contact number, or add a contact from your phone contacts list by tapping the Contacts icon at the bottom of the dialer screen.
Tap the phone-call icon on the dialer screen to initiate the call.