First of all, the Chinese Pinyin system is very different from the occidental languages, though they share the same letters of abc etc. The pronounciations as well as the composition are different. But when Chinese pick up a foreign language, they often learn it with the help of pinyin in order to master its pronounciation quickly. ( i know many beginners use this method.) For example, A can be noted as /ei/ in pinyin, and Sister as /seisite'r/ in pinyin. See? It's much like the phonetic symbols in English.
But it's not always helpful, and sometimes can be misleading. So the right way to learn a foreign language is to learn it by itself! Good luck!