You will need to follow the instructions provided by openvrtwitchchat to sign in with your Twitch Account so it can properly log into chat and display the messages to you.
Note that we (the Third Party Developer Forum) cannot assist with Application-Specific Issues and you should look elsewhere for support with an App.
To still answer your Question: An OAuth Key Token is a string that allows an Application to Authenticate itself against the Twitch API, similar to a Password, but it is specifically made for an Application with certain permissions only, so the user (you) can control what access to give to which Application.