Ebook

hi,I will explain my problem by the following sentence. Some questions has been added to this. They are not asked for answer,they will help you to understand my trouble.
"It is true that in a subsistence economy or even in a more advanced one when the person concerned can hardly make ends meet,money,or its equivalent reward,is of paramount importance-life,in fact depends on it."
What is the subject of auxiliary verb "is"?
What is the main clause of dependent clause that starts with "when the person concerned......"?
The end part of given sentence contains "it". To which "it" is indicating?
Long complicated sentence like this are often found in academic and legal texts. It can be confusing but I need to learn to filter all the extra information and focus on the core statement until I can identify the main idea,subject and verb.
I have completed a grammar course,and when I face this types of problem I try to solve them by applying all of my grammar knowledge. But sometimes it doesn't work. Sometimes proper explanation is needed to clarify them,which is possible by a skilled person.
Will you help me by providing the address of website/eBook/the name of other books which are enriched with proper explanation/exercise with solution or example,so that I can easily improved my skill on this.
Nousher Ahmed