(V): The action of placing an event or occurrence onto a calendar.

A Calendar is a thing were you can write down what you have to do like go shopping or if you are going to a party or something, I don't know.

It will help you remember what to do everyday so in my opinion
get a calendar!

what you use to know the dates

When making plans, to confirm that you have set the time and date, and entered it into your itinerary - you say it's been "calendared."

Useless pieces of paper. Whoever buys them shouldn't. Just get a digital watch.
Also, they're supposed to tell you the date. You should already know the date.
Never buy them. They are a waste of money.

To do what a calendar does; to calendar. Calendaring is the verb form of the noun, calendar. When you are calendaring, you are interacting with a calendar in some way.

A technique of temporarily “saving face” with colleagues, bosses, customers, and auditors by changing every calendar and clock in a particular workplace in an effort to cover up a missed deadline. “The Calendar Option” is the “Nuclear Option” of work place fault misdirection. “The Calendar Option” should only be used when the monumental task of changing dozens of calendars, clocks, and watches pales in comparison to actually completing ones assigned task on time. Hacking of local computer and cellular networks is usually preferred, as these sources represent the primary ways of determining dates and times. “The Calendar Option” will buy you enough time to prepare a resume, write a cover page, and apply for other jobs in the timespan prior to your superiors realizing you’ve elegantly gamed them to death. Worried about future employment? Don’t! One who can successfully employ “The Calendar Option” is often far under-employed anyway. This fact is clearly demonstrated as the time, energy, intelligence and sheer skill required to pull off the maneuver could be accomplished by no less than an American, tier 1, Special Forces operator who is also a Ninja.

Those times when you buy a new Calander before New Years. This is usually done a day or two after Christmas.

When you ring in the New Year on the toilet with one final dump, cleansing yourself from the old and welcoming the new. Starts on December 31st shortly before midnight.