You are welcome, its very simple and well used idea on Internet marketing.
Majority of these recurring payment services require you sign up with a real credit card, typically they charge $0 at first month, by doing this they can attain your credit card info and have you as their potential customer, an established strategy used by almost all service online.
Sure, you can just input your own credit card, you get free 1 month service, oh yeah cool, but when the billing time is due, you are risking your own card charging by them (2nd month to be exact), and sure, you can cancel this subscription at the end of 1st month billing time but, its boring as fuck to do this as u need to remember, u need to login, blah blah, and some companies may even block your card after then, as you are trying to milk them, by spending nothing.
I think u understand above, then:
So, smart people use so-called virtual credit card (VCC), VCC is working like a real CC, but u don't need to worry about the next things, as its a fake card. So an empty $0 VCC is typically $5, you buy one empty VCC and use VCC to register those service (like MOZ.com) instead of your own credit card, thus you are paying $5 this month, using the service, and don't worry about the next.