The main reason to join clubs is to take part in Championships. These are managed through the website but appear in-game for you and your friends to drive. Only Rally Championships can be created with clubs, Rallycross Events are not an option. Also, a Club can only have one active Championship running at a time.
When you want to create a Championship you’ll be given the option to generate one. Pick the number of Events (locations) and Stages for each and the website will do the rest.
Once your Events are generated you can customise them how you see fit. You can even run different car Classes in different Events.
Once you’ve got everything set up, hit [Create Championship] and you’re almost ready to go. Pick the start time and Advanced Settings and you’re away!