Woops, sorry I forgot to add their meanings:
1) brb=be right back
2) hw=homework
3) dw=don’t worry
4) btw=by the way
5) ikr=I know, right
6) lol=laugh out loud
7) wth=what the heck
8) ttyl/s=talk to you later/soon
9) gm=good morning
10) gb=goodbye
11) bb=be back
12) hth=hope that helps
13) jas=just a suggestion
14) otoh=on the other hand
15) iirc=if I recall correctly
16) gg=good game
17) gtg=got to go
18) gj=good job
19) rofl/lmao=other ways of saying lol