The help menu is the first place to look for information. Browse through topics, start using MusiCAD by using its tutorial, take a look at the visual help and click the item you want to know more about, skim the Frequently asked questions, keep an eye on release notes if you have been using MusiCAD before, have one more tips shown at program start.
Using the help menu you may also adapt the way MusiCAD will respond to your input by changing hotkeys
'About' will show you almost anything that is (more or less) relevant of your computer, Windows, your melody and MusiCAD.
To access the help file contents directly from Internet you can select Force Web-help in the file preferences dialog