For trains without reservations or with optional reservations, that QR code is all you need. It is your ticket.
For trains with mandatory reservations, you also need a reservation. Please take a look at this thread for ways to book reservations:
If you have any questions after that, then please mention route, date and departure time of any train you would like to book.
By the way, it is not a good idea to activate your pass, travel days or inbound/outbound journeys in advance. You never know what will happen and you can only cancel activation until midnight CET before validity starts. If something unexpected happens on your planned start day and you had already activated the pass, then it will be too late to change it. Therefore, only activate your pass on the start day, when you know your train is running and you are going to board it. Do the same with any new travel day (if you have a flexipass).