There's a lot of stuff!
"Throwing shade [on something]" is basically being negative or talking shit to / about that person or thing.
"Lowkey" is something you say when you don't want someone to spread something or you're admitting something you're ashamed of, like, "I know her breath smell like ass* but I'm lowkey feeling her."
"Feeling [someone]" is having feelings for someone or connecting with someone in some way, like getting along with them or understanding their emotions.
"Bare" means a lot, etc.
Most (though not all) of it is black slang that just spread out onto the internet. I think the spread might have had something to do with the rise of R&B? When it got more popular, what was cool changed and a lot of groups suddenly fused into what you have now. So you got "fam", "basic" (as in"basic bitch"), "bae", "lit", "on fleek" spreading, etc. Most are only really used humorously now, though ("Hurry up! We're going, fam."). And even back then, for words like "fam" or (the memories) "mandem", you only really had certain people who used them seriously (*cough*
roadmen *cough*). There's so much of this stuff.
Maybe use "on point" instead of "on fleek", because it stands out less and while it
will date, it's easier to swallow. Awesome is still good, but bear in mind that it'll paint your character as a certain kind of person (a lot of people I know wouldn't say "Awesome". "Great" works fine).
I think in every generation it's always been a bad idea to try to incorporate fad words because they drop out of usage so quickly, and only a few stick around. But it can work. I don't think certain voicey terms like "as fuck", etc., are going anywhere anytime soon.
Also I'd be careful about asking primary school kids (whatever age group that is in America?) about this stuff -- one thing I've noticed is that whatever they're using is what everyone else STOPPED using a year ago xD
*lol