Place the mouse pointer over a button or a controller and wait for the tooltip to appear. All tools have their own tooltip with a detailed description and the current hotkey:
Click on the question mark present on the top right of each UI panel.
Your browser will open a documentation page:
The contextual help panel shows you the principal actions you can do in the current edition mode plus gives you a list of the current mouse bindings:
Our channel is frequently updated with new help videos and tutorials:
You may start with this UI overview video.
Our forum is the reference place to post your request and bugs. It is also a great resource of Q&A on the software use: