There are four basic tones in Chinese. They are as follows:

Tone Number	Name	Pinyin Diacritic
1st tone	Yīnpíng	¯
2nd tone	Yángpíng	´
3rd tone	Shǎngshēng	ˇ
4th tone	Qùshēng	`

I was listening to some videos on iTunes U because I wanted to learn Chinese. The first few videos that I watched kept referring to an Nth tone and I was very much clueless what the person in the video was referring to. It wasn't until after I finished a few vids that I saw the one explaining what the tones were.