Is there a reference manual for cPanel?

Yes. Access your cPanel. Across the very bottom of the page you'll see a row of links. Click on Documentation. Once the next page opens, click on cPanel User Guide. Keep in mind that is is a generic document and some the features described may not be available to LinkSky members. 

You many also find the Help link useful for shorter explanations.

In addition, many of the features within cpanel offer a video tutorial and more are available here -- cPanel Tutorials.