Everything is link building. Buying advertisements is a link to your site. Every single thing ONLINE is link building. The only way would be to hang up posters on telephone poles around the world .
Starting out most people spend lots of time and effort on SEO and link building - to get free traffic from Google (+ Yahoo, Bing) Personally I think this is misguided - because of the enormous time and effort needed to drive traffic to a site or page that performs in an unknown way = probably doesn't do what you want or make you $. It's actually cheaper and much quicker to start buying some traffic to first test out a site. If it works - great spend time and effort on SEO with link building. If not better try something else - and you haven't wasted hours of work plus months waiting for traffic to come from SEO Otherwise starting out investing your time and effort on SEO and link building is no different from gambling - most of the time you lose.
If you have a good site with superb content and interseting topics of course you dont need to do linkbuilding - it is done by your visitors...... Otherwise: Yes, you definitely need it
Two main factor of SEO . Quality content and Back links.If you want to promote without these way . then use social media website or paid advertisement i.e Google adword.