One of the many plugin types used to extend a WordPress site are calendar ones. Many free and premium ones are available in the repository and elsewhere with a whole set of functionality from displaying simple dates to client booking for example. XO Event Calendar is a free plugin on the simpler side of the spectrum.
After a normal plugin installation the Events menu is added in the WordPress backend. XO Event Calendar adds its own custom post type and taxonomy (category). Each category can have its own background color on the calendar. In a similar way any number of