To make a call with drupe like initiating any action with drupe, just drag the contact you wish to call from the left side of the screen by long tapping its avatar, and then drop it on the green phone action icon in the app bar.
If you want to call a phone number which is not saved in your phonebook, dial the number from the drupe dialpad (the icon at the bottom left of the screen), then tap the button with the green phone icon.
Pro tip! You can long-tap the call button to start the call on speaker. Neat, right?
The optimal way to experience drupe is by setting it as your default phone app. You can do it by opening drupe settings > call screen > and set the Default dialer option to "Enabled". With that, your calls are initiated with drupe's call screen which features a built-in call recorder, conference call feature and much more😀🙃