I don't seem to see how you register? I have a Strava account but not sure how to link it.
You don't have to register at all, if you are on Strava, you can go to the explore tab, select clubs and search for the 'The People's Grand Tour' club and join it, but you don't have to, it will just show your rides in that club and on the PGT homepage.
You have to log the following for yourself over the course of the events:
Number of days ridden:
Number of kilometres covered:
Time in the saddle: (in hours and minutes)
Metres climbed: (optional)
Longest single ride:
Easier done with Strava or similar because it logs it all. Then just post it on the PGT website or email it to the site on the contact page within a few days of it finishing.
Then, assuming you did 10 days, you get a GC placing and a PDF certificate you can print out and bore people with
If on Strava, also join the Retrobike club.