A natural backlink is a link that a blogger adds into his blog or a webmaster adds into his website because they think that your informations on your website are important in relation of their website.
Search engines appreciate natural backlinks and their spiders are becoming more intelligent and the most important message that I want to tell you today is to not build thousands of backlinks in few days because it will take time to become a natural top search engine result.
Be careful when you submit your websites into directories or into other websites because you can be penalised from google if the argument is completely different from your website.
If you add interesting news into your website, people will start to find you on google research and if you have quality content, they will build backlinks for you sharing your informations into their blogs, websites and social media.