Find the icon for Help. Click it. What does it do? What are the controls?
OK, now you know that you don't have to discover anything more. You can look it up. How many of the questions you wrote down does Help answer? What kinds of questions remain?
The Undiscoverable: Well, what I told you isn't strictly true. You have just discovered that Help doesn't answer all questions. It isn't totally complete on the installed activities; it can't cover programming in Python, Turtle Art, or Etoys, or commands in Terminal and Calculate; and it has nothing to say about other activities you can install.
There are activities with their own Help functions. Keep an eye out for them.
Here are some more resources that explain parts of the XO and Sugar.