Question Make a simple Text chat

Dear Community,
I wish to make a simple text chat and i hope you can point me to a tutorial or point out a solution that covers the question.

There are some conditions:

a) Pure unity with the official networking solution (that is netcode for Gameobjects right?), no plugins or third party stuff.
b) The possibility to share private messages that are not shared with other clients and send byte arrays.

The focus of my question is on networking disregard anything of the ui, what is the way now to send a string or bytes over a network? I having really trouble to find good documentation on netcode for Gameobjects for this purpose. For me is the Documentation for netcode hard to read and it would be good to be improved too with examples and with more approaches to how to send data.
The topic seems to have ended up in the wrong forum, please move it to where it fits best.