Quite near to Bamburgh Castle is the starting point for these 'missions' - just check the world map for the exact spot.
As with the other Forza Horizon stories, you are tasked with completing different missions, earning 1-3 stars for each, dependent on how well you meet the criteria.
In The Car Files you are tasked by a German sounding fella to test some different, and some modified, vehicles regarding insurance claims to see if the claims are valid or not.
Although that sounds boring, it's really not and some of the modified vehicles and challenges you are given are quite fun.
I found myself smashing through the 10 challenges in one sitting.
Well worth popping back into the game if you haven't played it for a while.