Why are links vital in SEO?

My journey is the world of SEO just began a few weeks ago. I am not aware of most of the terminologies. I do not know how a web portal and blogs earn money. All I know that website is an easy way to reach to the masses. So, I thought of bringing my offline store to the World Wide Web. When I was going through different SEO blogs and forums, I came to know that links are very important for SEO. Can I know the reason? How are these links beneficial for a website?

===============================
Search Engine Optimization|Seo UK