A date in Sheets is a number: the days since December 30, 1899, shown with a date format. That's why you can subtract two dates to get days between them, and add 7 to get next week.
Functions take dates apart and build them:
YEAR(B2), MONTH(B2), DAY(B2) return the parts as numbers; TEXT(B2, "mmmm") returns the month's name.DATE(2026, 3, 14) builds a date from parts.EOMONTH(B2, 0) is the last day of B2's month; EOMONTH(B2, 1) the last day of the next month.EDATE(B2, 12) is the same day 12 months later, which is how renewal dates are worked out. From January 31, one month later is February 28.
Dates imported from other systems sometimes arrive as text that only looks like a date: it sits on the left of the cell and date math fails on it. DATEVALUE(A2) turns that text into a real date.