Date functions answer "how long" and "when" questions.
DATEDIFF('day', [Created Date], [Closed Date]) counts days between two dates. If either date is NULL, the result is NULL.DATEADD('day', 2, [Created Date]) moves a date forward by two days.DATETRUNC('month', [Created Date]) rolls a date back to the first day of its month.DATEPART('weekday', [Created Date]) returns a number; DATENAME('weekday', [Created Date]) returns the name, like "Monday".
Two traps. DATEDIFF counts boundaries crossed, not full periods: from January 31 to February 1 is one month, because a month boundary sits between them. And a date calculation dropped on a shelf lands as a year, like YEAR(Month Start): pick the level you want from its menu, or Exact Date under More.