One Illegal way to get backlinks is via paying money. But as we all know, Google and other search engines hate paid links and penalizes sites that sell or buy backlinks.
So if you cannot buy backlinks then how can you get any links?
The answer is simple: the simplest way of getting natural, free, pure, relevant, quality etc, backlinks is to write useful, accurate, up-to-date, informative and quality content and add it to your site. In this way, you will get both traffic and natural backlinks.
I said traffic and backlinks right? Traffic will come from different search engines.
Google love fresh and unique content and this is why, Google ranks such content high in the search results. So you will get lot of free traffic.
Backlinks will come from different websites. People who will find your content useful will link to your site.
This is the natural way of getting backlinks. No need to think about anything else when you can get links in this fashion.
People often try to get links via article submission. For this method, you will need some articles of about 300 to 500 words. If you cannot write articles, then you will need to hire a writer from any freelance site. Remember, the articles need to provide useful content. I personally will suggest to not spend time in article submission and instead spend the same time in writing content for your own site.
Organic links should be your first priority.
Add useful content in your site, and you will naturally get lot of backlinks.