Here’s some American slang if you didn’t know them already:
Jk

= just kidding
Hbu = how ‘bout you (or how about you)
Lol = laugh out loud (same as hahaha)
Omg = Oh my god (or Oh my gosh)
Wth = What the heck (or what the h*ll)
That’s tuff = It’s a joking way of sympathizing with you
Bruh = Showing disappointment or joking/light disappointment
Lmao = Laughing my *ss off (same as laughing very hard or something is very funny)
Istg = I swear to god (is said when they are being dead serious)
Also some common slang is also words shortened for example ‘you’ could be shortened to ‘u’ or ‘though’ could be shortened to ‘tho’

Now you know this, have fun haha