Its just a very basic database driven website.
The database stores all the event details then they are displayed with asp (or php). Adding an event put the info in the db.
The db would likely have fields for ID, Subject, EventDate, Location, Details and DatePosted and thats pretty much all there is to it.
The query string passes the page an ID number, then you look up in the db the details for that ID and display the data. IF there is no id number given display all the data. The add event just takes the form data an inserts it into the db.