Link building is essential to building a popular website. There are many ways to get links (a clickable button or word that sends people from one website to another) but some are much better then others.
The best way to get more links to your website are by providing something that is interesting, new, shareable, and useful. If people find it useful to themselves often they will share it with others. Think of finding a new restaurant, reading a new book, or going to the movies. When they are really good you tell your friends and family about them. The same process works online.
Links are important because they send immediate traffic from other website and also help Google understand how important you are based on specific subjects. For instance, if you are running a website about mountain biking and a very important bike company links to a recent article on your website Google will consider this important. It will also categorize you as being important in the bike world. The more of these categorizing links you get the better.
Links are simple really. Provide something useful and then start sharing with others. The more novel and unique the resource the more likely people are to share it. Then the more times they share it the more links you have. This provides immediate visitor increases and helps Google to know how important your page is. If your page is important it will send you traffic too. Links are very important for your website.