Auto-approved: The admin does not have to approve your link, it gets approved automatically.
Pending: The link is submitted into the system, and the admin can either approve it or deny it.
PR: This is a short abbreviation for PageRank. It is a number/score that google gives out to pages. It sometimes help pages rank well on the search engines as well (?).
I did not quite get your question "what is the basis of improving your project site". Maybe you can re-phrase it?
Here is a list of directories that are organized from high PR to low PR. These sites have administrators that actually approve or deny links. Some administrators make a directory and forget about, and in the end you see 50,000 pending links.
Hope that helped

