Welcome... first of all.. I think you may have the wrong impressions here (= assumption on my part!) because this environment isn't necessarily about editing stuff and such. But first: yes, you can add drawings to your Designer projects and then embed those into your project.
But please keep in mind that Designer isn't like any 3D sofware you may have worked with. This isn't necessarily about modelling and designing 3D and such, a better description in my opinion would be scripting. You basically build up a 'script' which consists of nodes; these act like individual building blocks. Each has a specific function or purpose, and put them together and, well, you can make magic happen.
Where to begin? First I can recommend the documentation. No, this isn't your classic "RTFM!" comment but "Help => Documentation" honestly leads to something good.
Second (bias goes into effect here!) I highly recommend following this YouTube playlist from the official Adobe Substance 3D website:
https://www.youtube.com/playlist?list=PLB0wXHrWAmCwWfVVurGIQO_tMVWCFhnqE
I think that has the full potential to both blow your mind and teach you some seriously useful basics on Designer.
Hope this could help!