Domain authority is a ranking score that predicts the likelihood of a website to rank on the SERPs. The concept was first introduced by Moz. At the moment, it is widely used in various SEO tools.
Domain authority is anywhere between 0 and 100. The higher the score is, the more likely you are to rank.
Domain authority is not one of Google’s ranking factors. It is mainly used to understand whether you are more likely to rank than your competitors and detect some issues with your SEO. If you got a higher score from Moz, it does not automatically mean that you will rank higher on search engines as well.
In order to improve the domain authority, you can work on your backlinks. It includes getting more relevant and high-quality links, avoiding links from unrelated or spammy websites.
Some other practices are increasing website loading speed, creating responsive websites, and building a good internal linking system.
As you can see, it includes all the good SEO practices. However, the most important thing is to still create great and presentable content that your audience likes. If you work for your visitors, you are more likely to rank higher than while working for search engines.