Seo stands for Search engines optimization which is an important process to get your site upper in search results. There is two kind of seo, inside and outside seo. We suggest you to care for unique contents, non unique contents may damage and spam your site. If you spammed then your site go down in search results.
It is hard to get more visitors from irrelevant backlinks. You should check the site you buy backlink from to see if its content fits your site. These kinda backlinks help your site to get better at search results. Seo is a long way according to your competitors.