When another website links to your site, this is referred to as a backlink, or inbound link, and these are an important aspect of SEO. Backlinks show that other websites have trust in your content and believe that you provide high-quality information that is of value to a reader. This means Google is more likely to rank you higher on the SERP.
It is vital that your backlinks come from authoritative websites – preferably with high traffic and high ranking itself. The links that you gain should be high quality and related to the industry you are in, otherwise this will be seen as spam or a paid link and you may be penalised.
There are many ways to gain backlinks from other websites, including writing a guest blog post, providing a quote, featuring within a review, etc. As well as ensuring you provide unique content in the form of video, a downloadable, a resources page and many more that people want to reference within their own website as they believe it will benefit their audience.