The short explanation is: you participate in virtual races, paying for registration and awesome Potter-themed medals; the money goes to charity. You can also use the free Charity Miles app to contribute your miles-aka-points to your chosen House for the Hogwarts House Cup. That translates into money for charity, too, and doesn't cost you a penny!
However you choose to participate--virtual race events, the House Cup competition through Charity Miles, or both--it's a great, nerdy motivator to get out there and exercise AND to do some good. Lots of the participants are über-marathoners who run miles and miles every day, which is awesome. But lots more are exercise n00bs like me who need this motivation just to do any exercise at all.
“The Final Inaugural ‘I Must Not Tell Lies’ Dolores Jane Umbridge Run 13k…Or Until It Sinks In.” I used this race as a motivator to exercise, not purchasing the registration / medal until I'd completed it. I chose to complete this race on my stationary bike at home, logging over 20 miles over the course of 3 weeks to get in the cycling equivalent mileage to 13K at the 2.5:1 rate HRC goes by.
For someone as out of shape and lacking fitness gumption as me, that was quite a feat. I completed my miles in the evenings after Avery went to bed, and finished my 20 miles in 21 days. I can't wait to get my medal (one of Umbridge's horrendously saccharine cat plates!) and I can't wait for the next event to motivate me to exercise!