Or, you can watch this short video to listen how to pronounce each tone.

https://www.youtube.com/watch?v=TnwOEBISYqU

Let’s break down all four tones and neutral tones.

First Tones : The first tone it starts high and maintains it for the whole process (rather monotone)

Second Tones : The second tone it starts in middle and goes up to high (English speaker usually associate this with rising pitch when asking question)

Third Tones : The third tone starts mid-low, dips down and then rise to mid-high

Fourth Tones : The fourth tones starts high and then immediately goes down 

Last but not least are neutral tones or in Mandarin qīngshēng (轻声). These usually occurs in the second syllable of two-syllable word or between two stressed syllables or even in phrases, but never at the beginning of a word. These will sound light, vague, unstressed and short. The general rule for neutral tone is that neutral tones always lower than the preceding tone, except for third tone, in which case the neutral tone is higher. Take a look at chat below for neutral tones changes for each tones and some example for neutral tones.

Tone changes for yī (一)

When followed by a fourth tone, yī (一) changes to second tone (yí). When followed by other tone, yī (一) changes to fourth tone (yì). 

There are some exceptions for this one, when yī (一) appears as a number, larger number, date, address, it is pronounced without tone change.

Tone changes for multiple third tones

When a third tone is followed by another third tone in two-syllable word, the first third tone changes to a second tone.