Mandarin syllables may be pronounced in five tones:
Tone 1. This is a long, high tone: 55. In Pinyin it is indicated by a - over the main vowel.
Tone2. This is a rising tone: 35. In Pinyin it is indicated by / over the main vowel. Note that it doesn't go the full way up from 1; it starts at 3.
Tone 3. This is most often a low tone: 21. However, a syllable on its own or at the end of the word is pronounced with a falling rising intonation:214. In Pinyin it is indicated by v over the main vowel.
Tone 4. This is a short falling tone: 51. In Pinyin it is indicated by \ over the main vowel.
Tone 5. This is a neutral tone; how it is pronounced depends on the preceding syllable. In Pinyin absence of a tone mark indicates the neutral tone.
In the above 5 indicates the top note of the normal range of your voice and 1 the lowest note.
妈妈 māma 'mother'
麻 má 'hemp'
马 mǎ 'horse'
骂 mà 'scold'
Be careful to get the tone right even if you are speaking quickly. There are many pitfalls e.g.:
火车 huǒchē ‘train’
货车 huòchē ‘van’
Influence of tones on each other
The neutral tone is pronounced:
lower after a syllable in Tone 1 e.g. 妈妈 māma 'mother'
lower after a syllable in Tone 2 e.g. 麻烦 máfan 'nuisance'
high after a syllable in Tone 3 e.g. 我的 wǒ de 'my'
low after a syllable in Tone 4 e.g. 谢谢 xièxie 'thank you'
In all these cases we may think of the neutral tone as being a continuation of the tone on the preceding syllable.
It can be very difficult to be sure whether a character should be pronounced with its tone or neutral. In this respect, the Pinyin in this resource is not completely consistent. In Taiwan, many syllables that would be neutral in Beijing are pronounced with their original tones.
Note that in this resource 一个 is Romanized as yí ge. This is Beijing dialect and reflects the pronunciation in the recordings; standard would be yí gè.
Several Tone 3s together
There are basically two possibilities, depending on which of the Tone 3 syllables form words. (I have indicated a word by _ in the below.)
Tone 3_Tone 3 + Tone 3 -> Tone 2 + Tone 2 + Tone 3
Tone 3 + Tone 3_Tone 3 -> Low + Tone 2 + Tone 3
Occasionally Tone 2 becomes Tone 1
If a syllable in Tone 1 or Tone 2 is followed by a syllable in Tone 2 and then a syllable in Tones 1, 2, 3 or 4, the Tone 2 in the middle syllable becomes Tone 1.