Why should you have backlinks in your website? Back links, better known as link building, help improve your SEO. Think of it like this, backlinks is more thought of the "vote of confidence" or "stamp of approval" from third parties. If other sites deem your content worthy, so will search engines. They want to rank sites higher that have more backlinks.
How do I get back links? Think of it as a referral... You need content to refer to. So, creating content, and content often will help people find your content more. Example: If you are a landscaping company and you are looking for backlinks, a simple example would be someone that posts a photo of your work on Facebook adds a link to your website. Also, someone can write a blog post that adds you as a source for more information.
Start building links, it will help you build your SEO tremendously. See high ranking competitors as well for examples as well to get your idea on which links help them rank higher.