"Rouge" goes on your face as makeup. A "rogue" is a D&D class, or someone doing something they shouldn't.
"Where" is a place, like where you are. "Were" is the past tense of "to be," like you were reading this list. "We're" is the contraction of "we are."
"Their" is a thing or concept belonging to a person, like their book or their justified anger. "There" is a place.
"To" is a conjunction, or a word used to make other words work. For example, you don't "go the store," you go to the store. "Too" is either an intensifier indicating an excess of something (like "too dark," "too cold," "too long"), or a word meaning "also" (like "I want to go, too"). They are not interchangeable.
--"a couple" is explicitly two. "A few" is three to five (unless you're using it for comedic effect, like describing a horde of ten thousand orcs as "a few").
And finally, a few that don't get discussed all that much these days but they'll make me very happy if you know them:
--"less" is for abstract, "fewer" is for concrete. I get less and less happy when I have fewer and fewer books.
--"can" is for ability, "may" is for permission, and the two have mostly become synonymous BUT if you're writing an old or uptight character, or a period piece, that change is recent enough you should still do it the "right" way.
--"lay" and "lie" are not actually supposed to be interchangeable. Even Merriam-Webster will tell you the rule here is bullshit (or as they more politely put it, "lay and lie have been tripping up English speakers for 700 years"), but if you want to know how to do it to at least try to make your grammar checker stop having a seizure, "lay" is transitive and "lie" is intransitive. In other words, "lay" is when action is happening and "lie" is when it's not. A sleeping dog lies because it's not going anywhere, but you're laying the table for dinner because you're actively putting things on it to lie--ha!--flat. The trick I learned in college was "we laid him to rest, and there he lies."
