Apostrophes in contractions

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 or years.

The reunion for the class of ’12 is tonight.

I am studying the music of the ’60s generation.