Well,
once you start the app, you go to the settings and you see 3 input fields.
The labels are "User ID", "Player ID", "Password", so pretty self-explanatory.
Your UserID is your account user id here on TrackBase. Hover over your username on the forums on in the user block on the ET tracker and you get the idea. Player ID is what you supplied and password is something secret that only you can see on your reservation page once you clicked the icon in the TBAPP column (or pasted the link in your url bar and exchanged the placeholder with your player id).
Do not forget to click ok / save and you should get the profile check successful message
/JoNny