You can easily register in the app. Then you can log in with that account and unless you log out, the app will keep you logged in.
Once you are logged in, it's time to start! Add the series that you like to keep track of. Now the app will gather all info of that serie.
Now you can see all the series you have added in your personal Series List.
You can mark which episodes you have seen. So you can easily see which episode to watch next!