Your Domain Authority is calculated based on all the links to your domain. For example, if you have one link with the PA (Page authority) power of 10 that links to your main page (https://www.whoisua.com/) and then one link that links to a specific subpage (for example this page https://www.whoisua.com/domain-authority-checker) with the PA power of 15 then the combined link DA power is summarized to 25.
Keep in mind that it is not a simple as a plus and minus game. It usually takes several links with PA 10 to achieve DA 20, a good estimate would be at least 30 links from sites with PA of 10 to get DA 20.
The more powerful the link you get the quicker your domain authority will increase. A link from a domain with DA 50 is in average worth more than 1000 links from a DA10. The reason for being so is that only a few sites are able to gain this high trust from google, and if you get a link from a page with high DA then Google will consider your site to be of high value since Google already trust the linking page this much.