We've known about iTunes Match for a while, but it just went live in the UK today. The £22/year music service promises to not only store your iTunes purchases in the cloud, but to back up your non-iTunes tracks as well. So how does it work exactly?
The first thing you need to do is make sure your iTunes is up-to-date -- 10.5.2 is the latest, which you can find here. If you need further explanation on how to install iTunes, give up now. As for the rest, well, walk with me.