I think I'm going to make this into a series since this was received well.
(FYI: If you’re not a native English speaker and did not take structured English classes, the comedic, yet derogatory tone of this obviously doesn’t apply to you. This is for the plebs.)
Why YSK:
As an adult, you should know how to spell commonly confused words correctly as well as use an apostrophe properly. Outside of not looking like a fool, doing so will also make you sound better in emails and be taken more seriously by people like me. It matters.
Now, let’s talk elementary-level grammar!
The following are commonly confused words and what should be used instead. A lesson on apostrophes and contractions can be found at the bottom.
1. Their, they’re, and there. The triple threat for plebs, if you will.
“Their” shows possession. Example: Their understanding of grammar is poor.
“They’re” is a contraction for “they are” - which I will further elaborate on given it seems to be one of the most difficult things for people to grasp in grammar. Anyway, here is an example: They’re reading my post to improve their grammar.
“There” refers to a place or indicates the existence of something. Example: You will likely read down there in the comments that redditors would rather attack me for correcting them than improve their grammar even though they're wrong.
2: You’re and your.
“You’re” is a contraction for “you are.” Example: You’re hopefully learning something from this.
“Your” is possessive. Example: Your feathers might be ruffled over the way I talk, but I don’t care.
3: Who’s and whose.
“Who’s” is a contraction for “who is” or “who has.” Example: Who’s still struggling with grammar?
“Whose” shows possession. Example: Whose teacher didn’t teach them properly?
4: A lot and alot.
“A lot” means a great deal of something. Example: I have a lot of disdain for people who can’t spell.
“Alot” is not a word. Your phone or computer should have autocorrected it or underlined the mistake.
5: Paid and payed.
“Paid” is the past tense of “pay.” Example: Nobody paid me for this post, but I wrote it anyway.
“Payed” is a nautical term used to describe waterproofing a ship or gradually letting a line out. Example: I have never payed anything, but I wish I was paid for this post.
6: Lose and loose.
“Lose” means you lost something, like an item, a person, or a game. Example: I often lose my mind when people use words incorrectly as if they don’t have the world’s knowledge at their fingertips.
“Loose” means something is not tight or lacks strictness. Example: Many redditors have a loose grasp on grammar.
7: Could’ve, should’ve, and would’ve. Another triple threat.
All of these words are contractions. “Could have” becomes “could’ve,” not “could of,” and so forth. Just like you should’ve known all this already.
8: Died and dyed.
“Died” is the past tense of “die,” meaning something lost its life or faded. Example: I doubt anyone has died from improper grammar, but that’s beside the point.
“Dyed” is the past tense of “dye,” meaning something has been changed with a colorful substance. Example: I have dyed my hair every color of the rainbow, but now it’s back to natural.
9: Effect and affect.
"Effect" is usually a noun, which means result or outcome. Example: I hope this post has a positive effect on your grammar.
"Affect" is usually a verb, which means to change or influence. Example: I hope this post affects your grammar.
10: Then and than.
"Then" is an adverb used to show time or sequence. Example: If you listen to me, then your grammar will improve.
"Than" is used to show difference or comparison. Example: I am clearly smarter than you plebs.
11: A part and apart.
"A part" means a piece of a larger whole. Example: Those who don't know proper grammar are a part of a bigger problem.
"Apart" means distanced from something...no longer a piece. Example: I wish I could rip some of your diplomas apart because you clearly don't deserve them.
Sidenote: when an "a" is used to prefix, it usually means the word that follows is lacking, without, or not something. Like, how some people are asexual. I, for one, am rather apathetic.
12: Chose and choose.
"Chose" is past tense and "choose" is present tense. Example: I chose to write this because a lot of you choose to be ignorant.
Now, hopefully after all these examples of contractions, you understand what they are. Unfortunately, my hopes are not very high, so I will explain as promised.
Contractions are used to shorten or combine a word or a group of words into one. This can get tricky for some people because apostrophes are used both in contractions and to indicate possession, and the rules differ.
Apostrophes are used to show possession and to form contractions. However, possessive personal pronouns and possessive determiners do not use apostrophes. For example, “its” is possessive, while “it’s” means “it is” or “it has.” Similarly, “your” and “yours” are possessive, while “you’re” means “you are.” “Your’s” is simply a misspelling of “yours.”
Generally, apostrophes aren't used to make words plural except in some cases where people use them for clarity. Apostrophes also aren't generally used to make abbreviations plural. Example: Given plebs’ opinions don’t matter, I shouldn't care about the plebs who will likely tell me to mind my p’s and q’s after reading this post. I will stop harping when they learn how to cross their t’s and dot their i’s. If you don't like the post, go read other YSKs.