What Counts As A Backlink? How Do I Get More Backlinks? What Should I watch out for?

Duplicate content can be copied from another site or the same content repeated on your own site.

As much as I wish I completely understood how Google works, I can only speculate...

As Google crawls websites it downloads the content and keeps it on Google servers. Then I assume it keeps crawling and if it sees the exact same content it makes a judgement about who had it first and penalizes the site that copied.

If you create multiple pages of the same content on your own site, Google will take that as you trying to trick it by loading up your site with the same stuff repeated. That is why people use robots.txt files to tell Google and other search engines which folders to crawl and not to crawl. This helps avoid duplicate content issues.