Mandarin Chinese has four tones, not six.
Here's why:
* The four tones are: High, Rising, Dipping, and Falling. They are represented with numbers (1, 2, 3, 4) for ease of learning.
* The "sixth tone" is actually a neutral tone. It's not technically a "tone" but rather a lack of tone. Words with this tone are usually short and unstressed.
It's important to distinguish between the four tones and the neutral tone to understand how Mandarin pronunciation works.