There have been several ways devised to use the Roman alphabet to write Mandarin, and the most official of them in called Hànyǔ Pīnyīn [link], though there have been others. But it is apparently used far more by Westerners to learn Chinese than it is by the Chinese themselves, who seem to be very much wedded to their character system, though they are willing to use simplified versions of that.
At any rate, if you are interested in learning Mandarin, or think you might be in the future, do hold on to this video and this URL that goes with it:
Quibcag: Yep, it's Kagura of Gin Tama (銀魂 Gintama, lit. "Silver Soul") again.