You either start a group message or join one when someone in a group texts you. I don't know what messaging app you are using or if it's up to date being on such an old phone. You also don't get security patch updates any more. It's beyond time to get a new phone. KitKat was replaced in 2014.
You're right, I've been looking. I want something on the smaller side that's 5G capable on either AT&T or T-Mobile since I use a bundler.