Sorry for not responding before, I have missed your discussion when I checked yesterday.
Twitter requires a Token which authorizes an application to access to the account of a user.
To create a Token, Tweetinvi provides the TokenCreator class which will first give you a web location (on twitter.com) the user will have to go to enter its credentials.
When the user has validated the application Twitter will provide a key the user will have to enter in order for the TokenCreator to generate the Token.
There are examples in the Examplinvi project (to get Examplinvi download the source code). Also if you want more information concerning the TokenCreator you can go
For general information concerning the Token and how they are generated please look at this
Let me know if you have any other question or if you need more details.