To call a contact in drupe:
Drag & Drop: Long-press the contact’s avatar on the left side of the screen, then drag it onto the green phone icon in the app bar.
To call a number not saved in your phonebook:
Open the drupe dial pad (icon at the bottom left of the screen).
Dial the number, then tap the green phone icon to make the call.
Quick Call Tip:
Enable the "Double-tap" feature (Settings → Personalize → Double-tap) to call a contact by simply tapping their avatar twice.