With this offer, you sign up for an account and provide financial details. The trial automatically activates a subscription ie bills your credit card after the three-day period has expired, so you must cancel the auto-renew setting if you do not want your trial to convert into a monthly subscription. Full details are provided in the T&Cs, so be sure to read and understand them. It's not an overly complicated process, nor is it an unusual arrangement for online free trial offers, but I frequently see posts in genie forums from people complaining about how they didn't understand the auto-renew set up and/or hadn't read the T&Cs.