Pinyin

In 2003, in northern China, archeologists found tortoise shells dating to 6600-6200 BCE which had geometrical carvings similar to ancient Chinese characters.  Remarkably, the next example of Chinese characters doesn't appear until 5,000 years later, when animal bones dating to 1200 BCE were found carved with information about the Shang dynasty. The general consensus is that the tortoise shells were just symbols, that proto-writing developed around 2000 BCE, and that true writing* was already established by 1200 BCE.

This is actually quite late compared with Mesopotamia, where proto-writing developed around 3400-3200 BCE with Sumeria cuneiform, and was true writing by 2600 BCE. (It is unclear if Egyptian hieroglyphics developed independently around the same time, or were influenced by cuneiform.)  Around 1850 BCE, the semitic tribes took hieroglyphics and converted it into a written alphabet based on sounds.  For example, the Semitic word for "house," bayt, starts with "b", so the Egyptian hieroglyph for "house," per, was used to write the sound [b]. The advantage is that, because there are only a limited number sounds the human mouth can make, there were relatively few letters in the alphabet. (The disadvantage is that the word has no relation to the object, and as languages developed and diverged, the words changed until they were completely different.  This is how Hindi, French, and English can all be descended from the same language.)

(In Mesoamerica, proto-writing began around 900 BCE, and developed into true writing around 600 BCE.  These are the only known instances of writing developing independently.)

Like hieroglyphs, Chinese probably started as "pictograms" where each character represented an object, but evolved into "logograms" where the characters became more abstract and represented ideas, which could then be put together to express more complex or nuanced ideas.  In modern Chinese, there are over 4,000 characters, although only around 2,000 are generally used. The advantage of this system is that it is easy to guess the meaning of a word based on its underlying letters.  In addition, because pronunciation is completely divorced from the character, as spoken languages diverge and words are pronounced differently, they are still written the same.

The disadvantage is that to be fluent, you have to know 2,000 characters!  You can't work out a word by its spoken sound, and you can't "guess" at a letter.  It is also rather hard to fit 2,000 characters on a keyboard.

As early as 1605, Jesuit missionaries began writing Chinese words using Roman letters, but it wasn't until the Communists -- trained in Moscow in the 1930s -- introduced a phonetic alphabet which became known as "Pinyin."  In 1940, Chairman Mao made Pinyin an official language, it began to be taught in schools, the plan was to completely replace Chinese characters!  However, it hit one snag: Pinyin was based on the pronunciation of Mandarin Chinese, and so would have required speakers of all the regional languages to learn Mandarin first!

Fortunately the plan died out and Chinese characters are alive and well.  However, Pinyin is still widely used to help Westerners with place names and to help with basic pronunciation.  The problem is, the Roman alphabet isn't very standardized, and pronunciation for the letter "b," for example, widely differs between English and French, while "x" is pronounced differently between Italian and Portuguese!  . So while "f," "l," "m," and "n" are pronounced like their English counterparts, here are some examples (all from Wikipedia) to scare you:

Pinyin		English pronunciation
b		unaspirated p, as in spit
d		unaspirated t, as in stop
g		unaspirated k, as in skill
h		roughly like the Scots ch, as in loch
j		No equivalent in English, but similar to an unaspirated "-chy-" sound when said quickly. Like q, but unaspirated. Not the s in Asia.
q		No equivalent in English. Like punch yourself, with the lips spread wide with ee. Curl the tip of the tongue downwards to stick it at the back of the teeth and strongly aspirate.
x		No equivalent in English. Like push yourself, with the lips spread and the tip of your tongue curled downwards and stuck to the back of teeth when you say ee.
zh		A sound between choke, joke, true, and drew, tongue tip curled more upwards. Voiced in a toneless syllable.
ch		Very similar to nurture in American English, but strongly aspirated.
r		Similar to the English z in azure and r in reduce, but with the tongue curled upwards, like a cross between English "r" and French "j".
z		unaspirated c, similar to something between suds and cats
c		like the English ts in cats, but strongly aspirated
-i	-i is a buzzed continuation of the consonant following z-, c-, s-, zh-, ch-, sh- or r-. In all other cases, -i has the sound of bee.
e	a diphthong consisting first of a back, unrounded semivowel (which can be formed by first pronouncing "w" and then spreading the lips without changing the position of the tongue) followed by a vowel similar to English "duh".
ai	like English "eye", but a bit lighter
ei	as in "hey"
ao	approximately as in "cow"; the a is much more audible than the o
ou	as in "so"
ang	like song in some dialects of American English
er	like "bar" in American English
ia	like English "yard"
ie	similar to the initial sound in yet
ian	like English yen
u	like English "oo"
uai	like as in why
un	like the English won

In addition, spoken Chinese--unlike English--is a "tonal" language, where the same sound has different meaning based on the stress. The tone can be "flat," "rising," "falling," "rising-falling," or "neutral."  (I'm not sure the difference between flat and neutral.)  Originally Pinyin did not indicate the tone, so the words for “mathematics” and “blood transfusion” would be spelt the same!  Fortunately diacritics (accents) were added to the letters, but as English speakers aren't used to these, either, it doesn't provide much help.

As you can see, Pinyin is a hybridized solution that is not particular suitable for any Westerner, and then only allows one to speak Mandarin, not any of the other 9 regional dialects spoken in China!  (Although to be fair, thanks to the Communists most people know Mandarin, and there are over a billion native speakers.  However, they will probably be much more interested in practicing English with you than listening to you butcher Mandarin.

Finally, to paraphrase a brilliant essay on this:

Thus, relative to other languages, Mandarin is simply hard to master for the average English-speaker.  English, in contrast, is mercifully easy for the foreign learner. English lacks gendered nouns, so there is no need to remember that “sun” is male and “moon” is female. English also boasts a remarkably simple and flexible grammar system, a heritage of its Anglo-Saxon roots. English is a mutt of a language, a strange concoction of Germanic Old English, Viking Norse dialects, Norman French, and a bit of Greek, meaning English not only has an impressively rich vocabulary, but is related to a large number of the world’s most common languages. Mandarin, on the other hand, is only related to Tibetan and Sherpa.

* Proto-writing are things like information signs, which are simple ideas which require you to already understand the context.  True writing allows someone to express a complex idea that another person can reconstruct.