what an apostrophe is normally used for, to show possession
As someone who has learned bits of multiple languages I'll push back on this: contractions are an apostrophes main purpose in both English and every other language, it's the possessive use that's weird. (I should be clear that I'm counting languages that use an apostrophe to denote a gutteral sound in the middle of a word as being basically a contraction, as that's generally what they get kinda pronounced as in English)
I bet if you Google it then it's gonna turn out the possessive is an ancient ass contraction