Link building is one of the most important features of SEO, which is about increasing the amount of visitors to your website in order to make it popular within the search engines. Without link building, the search engines think that you don't really have much to offer and for that reason won't rank your site in the best positions in the search results.
Your website can have the best content, but without any inbound links (links direct to your site from other sites) that content will lost in cyberspace. Inbound links can be from any site. But it is much better, if an inbound link is coming from a site that is related to yours. In most cases, you either need to buy these links or you need to have very good content so others can link to it without asking them to link to your site.
Easiest way of obtaining inbound links is directories. There are many web directories available for free submission of your link. Also there are article directories, where you can submit your articles that includes link to your website.
So why inbound linking or link popularity is so important. This is because, search engines ranks site that are popular. In other words, sites that have a lot of inbound links. Basically, when you conduct a search for a term, search engine list the results according to popularity of the site and the content. So if site A is more popular than site B, search engine will put the site A above site B. However, you need to keep in mind, link popularity is not necessarily means quantity of the links directing to your site, it means quality of the links. So link popularity is measured by quality of the links that is coming to your site.
Usually quality link building takes more time and even with Link building Services it can take time. Also you may need to spend some money if you want links from specific sites. But, if you provide good content to your visitors, you can get quality links without even asking or paying when you buy high PR links for your website.