I played d2 20 years ago, getting back into it now on the switch. How in the world do you communicate with others? I cant even figure out how to add players i run into to my friends list? The pre selected communication is ridiculously limited.

Only communication method is via emotes. By default, emoting is bound to holding down the right joystick.

To add people you recently played with, you can go to your "Add Friend" page, you can do "Search for Users You've Played with".