MM Dear:
I have an ongoing set of video tutorials on YouTube which start with setting up OpenToonz to look (and mostly function) like Toonz Harlequin. This setup includes the "Drawing" tab.
Why Toonz Harlequin? Because all of the available documentation is for Toonz Harlequin - and, the developers of OpenToonz are working as we speak to make OpenToonz as much like Toonz Harlequin as they are able to do.
Start with this setup video - and then follow the videos in sequence (by date) to get a good education in using OpenToonz:
I hope these help you,
Greg Smith