New to Illustrator scripting, looking to make a Compound Path from Existing Paths/Compound Paths

I am wondering how to select existing paths (normal paths and compound paths) and make a new compound path.  Google does nothing for me on this....

I have begun to understand the basics of targeting objects and doing some basic changes such as width, height, textFont, positioning and such...but the Scripting Guide is hard for me to wrap my head around as far as compound paths.

I am also having issues understanding the differences between object references that either do or don't have an "s" at the end. I assume there is some uniformity to why many object references have both. Could someone explain the reasoning?

Example

pathItem

pathItems

Thanks in advance!!

James