Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Use an apostrophe to mark omissions in contractions and numbers
The apostrophe
Punctuation

In a contraction, the apostrophe takes the place of one or more missing letters. It’s stands for it is, can’t for cannot.

It’s a shame that Frank can’t go on the tour.

The apostrophe is also used to mark the omission of the first two digits of a year (the class of ’20) or years (the ’80s generation).