Pinyin is a system of writing the sounds of Chinese using English letters. It is fairly straight-forward, with each letter or group of letters corresponding exactly to a sound represented. Unlike English, however, there are no exceptions. Once you get it, you will have all you need to write down any sound you hear. While it is not particularly helpful for reading (except in the very beginning), I can’t imagine trying to learn how to speak Chinese without it.
The good news is that there are only 404 (or so) syllabic sounds, or consonant-vowel combinations. If that scares you, remember that in English there are thousands of different consonant-vowel combinations used to make close to 200,00 different words.
For those of us who use non-character-based languages, pinyin is a valuable tool to teach us how to say the language correctly. Since the correspondence between sound and writing are exact and unchanging, there’s never any confusion as to how to pronounce a word written in pinyin. When you’ve learned how to say the 404 (or so) syllables correctly, you’ve learned how to “speak” Chinese.
And now for the bad news: certain English letters are attached to sounds they are not associated with in English, so it takes a bit of re-education to learn what sounds they represent. For example, q is used to represent the sound that could be written in English with “ch,” and x is used to represent a sound that would be written with “sh.”
The best way to master pinyin is by using a pinyin sound chart, which can be found in most beginning language books (including my book, Survival Chinese Lessons). Make it a matter of priority. Do not adopt the attitude that clear pronunciation is unimportant so long as you get your meaning across.
Remember that your goal in language learning is to speak the language correctly, not just to speak it.