Here you can find a starting point in using QCAD. You got a Basic Construction workflow and a Basic Editing workflow. I think i don’t need to go in much detail because this workflow works in almost every aspect of QCAD so master this first.
At the end of the file there is a Hotkeys List which you can print and keep it next to you as a reference. I will stress on learning the Hotkeys and use them because your speed will be so much increased and you will be more productive.
VERY IMPORTANT: If you want to learn anything, click the buttons, try things out, check the manual and PRACTICE ! This is the most important thing, PRACTICE!!!