How will it help my SEO (Search Engine Optimization)?
Links pointing towards your site is vital for any sites SEO. Having backlinks from sites that are considered authority sites based on their PR will help you rank higher in the search engines. Not only will these links get you placed higher in all the major search engines, but it will sky rocket your own pagerank and website sales.

What is Dofollow?
Well there’s nofollow and dofollow. Nofollow links tell the search engines to not go any further and not give your site credit for the link that is placed. Dofollow is the exact opposite. Dofollow tells the search engines that your site is credible and in turn you get some “link juice” from each dofollow link.

(source: monsterbacklinks.com)