While residents across China use the same written character system, the way the words are pronounced differs from region to region. Standard Chinese is Mandarin or Putonghua, and it consists of five pronunciation tones. As a student of the Chinese language, the hardest part to differentiate is first, second, and fifth tones.
In 1958, the Chinese government rolled out its Romanized version of Mandarin. Prior to that, there were several different methods to sound out Chinese characters using English letters. Over the years, pinyin has become the standard around the world for those wishing to learn to properly pronounce Mandarin Chinese. This is how Peking became Beijing (which a more accurate pronunciation) in pinyin.
Using characters, people simply know that that character is pronounced with a certain tone. In Romanized pinyin, many words suddenly had the same spelling, and it became necessary to designate tones within the word to differentiate them.
Tones are of vital importance in Chinese. Depending on the choice of tone, you could be calling for your mother (mā) or your horse (mă). Here's a brief introduction on the five vowel tones in the Mandarin language using the many words that are spelled "ma".
First Tone: ˉ
This tone is designated by a straight line over the vowel (mā) and is pronounced flat and high like the "ma" in Obama.
Second Tone: '
This tone's symbol is an upward slant from right to left over the vowel (má) and begins in the mid-tone, then rises to a high tone, as if asking a question.
Third Tone: ˇ
This tone has a V-shape over the vowel (mă) and starts low then goes even lower before it rises to a high tone. This is also known as falling-rising tone. It's as if your voice is tracing a check mark, starting at the middle, then lower then high.
Fourth Tone: '
This tone is represented by a downward slant from right to left over the vowel (mà) and begins in a high tone but falls sharply with a strong guttural tone at the end like you are mad.
Fifth Tone: ‧
This tone is also known as the neutral tone. Has no symbol over the vowel (ma) or is sometimes preceded with a dot (‧ma) and is pronounced flatly without any intonation. Sometimes it's just slightly softer than first tone.
There is another tone as well, used only for certain words and is designated by an umlaut or ¨ or two dots over the vowel (lü). The standard way of explaining how to pronounce this is to purse your lips and say "ee" then end in an "oo" sound. It's one of the hardest Chinese tones to master so it may help to find a Chinese-speaking friend and ask them to pronounce the word for green, and listen closely!