Backlinks are still one of the strongest signals Google uses to decide how trustworthy and relevant a website is. A backlink is basically when another website links to yours, which tells Google that your content is worth referencing. The difference now compared to a few years ago is that quality matters more than quantity. One link from a well respected website in your field is worth more than fifty links from random low quality sites. Google has become much better at detecting links that are bought or manipulated, and those can actually hurt your rankings instead of helping.