Currently, the only way to draw with friends is to enter a Room.
To create or enter a Room, click the video icon on the left-side control bar.
If you don't see a room, you can click the "Create a Room" button to make a new room.
Once in a Room, choose the draw icon from the tool bar at the bottom:
Tapping this icon will add a whiteboard. With the whiteboard, use your trackpad or mouse to start drawing!
To learn more about using the whiteboard, head here.