Back in the earlier days of SEO, you could dramatically boost your ranking with backlink sharing.

Backlink sharing could be done by two websites partnering, you purchasing backlinks, etc. People would do this because a few years ago Google would use backlinks as a major factor in determining your page rank. However, as years pass Google has updated their algorithm (panda) where backlinks have a lesser role in determining how Google rankes your page.

With that said, backlinks can help your pagerank. However backlinks play such a minor role in the rank determination that it's not worth your time to buy backlinks or email tons of website owners to try and set up link sharing.

How should I use backlinks?

Just let them accumulate naturally. The most important thing to do is focus on making your content unique and interesting. As people become interested in your content you'll accumulate plenty of backlinks.