Guide for Date Functions?

Summary: I am trying to add validations on Action dates and need to parse out the day of the week.

Content (required): I am trying to add validations on Action dates and need to parse out the day of the week; so I can check that the date is not on a weekend. I was hoping for some guide or documentation on what functions were available and how I could get the data I need for my rule.

Version (include the version you are using, if applicable): 21C

Code Snippet (add any code snippets that support your topic, if applicable):