@Sally1104
You can do 2 ways. If you want to restrict days of the week for the entire calendar (Mon, Tues, Wed, etc.) then go to:
Calendar
Availability
Scroll to more Availabilty Settings
If you want to restrict specific dates on the calendar, then you will need to turn on Pro Tools and use a Rule Set to do that. This will only restrict the dates you apply the rule set to and will override your default settings on the Calendar.