You can register for all races in our Project Cars 2 series at ClubRegistration.net. You'll sign up for a series and that will automatically sign you up for all events (you don't have to drive in all events).
If you are an Xbox One user, you should register here: https://clubregistration.net/events/signUp.cfm/event/8810
If you are a Playstation 4 user, you should register here: https://clubregistration.net/events/signUp.cfm/event/8811
If you are a PC user, you should register here: https://clubregistration.net/events/signUp.cfm/event/8809
You can register for more than one series if you have more than one of the platforms. Unfortunately drivers on one platform won't be able to race against drivers on another platform at the moment.