Usually most cable companies who give you hardware to rent (modems/routers, or combo) will automatically secure it for you and have a randomly generated password and their basic username for you to use.
But it's been said already but I'll echo, Google is your best friend and usually simplifies things for you. So secure your Network and keep the password handy and remember what you named it (pick something silly !)
Also here is the support page for the error you received.
https://tera-support.enmasse.com/app/answers/detail/a_id/255/~/error%3A-0008%3A0000-you-have-been-disconnected-from-tera
Once you get back to us with your secured Network you can update us on anymore issues!
But it's been said already but I'll echo, Google is your best friend and usually simplifies things for you. So secure your Network and keep the password handy and remember what you named it (pick something silly !)
Also here is the support page for the error you received.
https://tera-support.enmasse.com/app/answers/detail/a_id/255/~/error%3A-0008%3A0000-you-have-been-disconnected-from-tera
Once you get back to us with your secured Network you can update us on anymore issues!