Tones

One way of looking at Mandarin’s four tones for an English speaker is by using various ways of saying the word "man."

First tone, a high and even tone: Oh, mān, why did you do that?
(Another way of thinking of this is an opera singer: Ahhhhhh!)

Second tone, a rising tone, as in a question: What did you see, mán?
(Another way of thinking of this is a question: What?)

Third tone, a flat, dipping tone: Come on, mǎn, you can do it!

Fourth tone, a falling exclamation: Màn, is that hot!
(Another way of thinking of this is when you stub your toe and scream, Ouch!)

Let's look at some visual images of tones. Note that they are normally placed against a scale of 1 to 5. This represents your voice's natural range of pitch. Everyone's pitch is different, and so your first tone will not be the same pitch as mine, but the direction will be the same. Third tone is normally represented as rising, but it doesn't actually rise as much as that. For a better representation look at the second image, which also includes a nice representation of neutral tone.

from https://web.mit.edu/jinzhang/www/pinyin/tones/index.html#single

from https://cls.arizona.edu/chn/chnpro/mtone/mtone.htm

Neutral Tone
The neutral tone sometimes (not alway) occurs in the second syllable of a word, and particles are normally pronounced with the neutral tone. In pronouncing the neutral tone, your voice simply reverts to its natural level. Listen to the following. Take note of how the voice bounces back to a natural level. In each case, the question particle 吗 ma follows a word, creating a question.

Tone Changes
As seen in the images above, in addition to the neutral tone, there are several other special situations in which the basic tone is modified (called tone sandhi or tone change). For syllables involved in a tone change, the actual pronunciation of the tone depends on the tone that precedes or follows it. There are three main tone sandhi rules.
1. If a third tone is followed by another third tone, it changes to a tone similar to the second tone. For example: hěn + hǎo = hěnhǎo 'very good', but it would be pronounced more like hen2hao3.
2. If a third tone is followed by a neutral tone, first tone, second tone or fourth tone, it changes to what is called a 'half-third.' It begins to dip, but never rises. For example:
hǎo + de = hǎode 'good' + a particle'
hěn + gāo = hěngāo 'very tall'
hěn + cháng = hěncháng 'very long'
hěn + kuài = hěnkuài 'very fast'

What this means is that the only times a third tone is fully pronounced is either when it is at the end of a term, or when it stands alone.
3. Before a fourth tone, the typically fourth tone bù 'negative marker' changes to a second tone. So bù + kuài = búkuài ‘not fast.’
4. The number one ‘yī’, first tone when alone (as for example when counting, or at the end of a term), also changes. When followed by a fourth tone, it becomes a second tone (just as bù does). When followed by another first tone, a second, or a third tone, it becomes a fourth tone.
yī èr sān = One, two, three
sānshíyī = 31
yī + kuài = yíkuài ‘one piece’
yī + zhāng = yìzhāng ‘one sheet’
yī + máo = yìmáo ‘one dime’
yī + běn = yìběn ‘one volume’

Recommended Reading
https://web.mit.edu/jinzhang/www/pinyin/tones/index.html

Let's start by looking at and listening to what the four tones sound like.

First are some visual representations of the tones, followed by the sounds.

Note that while it is essential to be able to to hear and produce each tone, most Chinese words are comprised of two characters, which means we normally hear and produce the tones in combination,
Here we hear the four tones in order: gāo (tall); máng (busy) hǎo (good); lèi (tired). (Recall from the section on pinyin what the tone marks look like.)