question Services that only charge when you get the domain?

[Hashim]

I'm a beginner to domaining in general, but there's a .co.uk domain that I like and that I really want to get hold of. I heard there are drop catching/backorder services that you only pay for when you successfully get a domain? Is this true, and what are these services if so?

Also, when's the best time to put a backorder on a .co.uk domain? Thank you very much, I appreciate the help to a beginner.