The apostrophe can:
1) substitute for a word/space in a contraction.
2) show possession when placed at the end of a word and followed by 's', save for words that end in 's' or the word 'its'.
3) be used instead of a 'g' in the progressive tense (is doing, was doing, etc.).
1) He's climbing pretty rapidly.
2) Stephanie's shorts were too small, but nobody complained.
3) I'm checkin' e-mail.
1-A punctuation mark used by morons and idiots to pluralize words or to conjugate verbs in the third-person singular form.
2-A punctuation mark used to show possession of something.
3-Shows omission of one or more letters within a contraction
4-(American system) Used to set aside quotations within quotations.
1-He want's to see his parent's.
2-"Bob's X"==the X belonging to Bob.
3-couldn't, they're, he'll, I'm, you'd
4-Then, Mark said, "Dude, I hate to tell you, but Sheila said 'I wouldn't go out with him if he were the last man on earth.' Tough break, man."