Back links is a incoming link that points your website from other website. High quality back links helps you to increase your websites DA and PA and also helps you to increase your keywords position in SERP.
If you are in need of quick results then you can go with SEM. SEM is a paid marketing where you need to pay and promote your website. Next, SEO is slow but steady it is an organic method to bring traffic to your website where you no need to pay money. This is the difference between SEM and SEO.
Hi, Check whether your website is connected with google webmaster. If not connect with webmaster first. The second thing you need to do is link building, get backlinks from high-quality websites to rank top in the SERP.