Marking calendar days

Do you have a question? Post it now! No Registration Necessary.  Now with pictures!

I did a very basic calendar in php, and know I want to mark some days.
For example: -exam days, semesters, etc.
What is the best way to do this?
I want to click a link, button, checkbox,etc and marking days to a
database, either single or start and end days.

Best regards,

Site Timeline