Here is a very simple explanation of asian chile pastes
and some substitutions, just scroll down to the section on chile paste. And, here is another explanation
. In reality, the ingredients in Chinese chile pastes vary by region and brand (and that doesn't get into the other variations from other Asian countries) - just like jars of "authentic Italian style" spaghetti sauce.
There are several recipes for fundamental homemade "Asian style" chile pastes out there on the web - but it takes some time to ferret them out, and my searching only scratched the surface. Here is one
- here is another
. There are others that contain ingredients which might be just as hard to find as a jar of chile paste, and are more regional/national to areas south of China that I didn't bother to list.