Page Authority (PA) is a metric, provided by Moz, that predicts how well your page will rank in Google's search results. The score is based on a 100 point scale and uses different variables such as the amount of links you have to calculate the score. For higher ranking pages, PA will typically be higher than your Domain Authority.
The best way to improve this score is to check the errors on our auditor first. If you have missing meta information or missing "alt" tags, those are relatively easy fixes you can do. Other SEO techniques such as building more relevant and authority links to your page will slowly improve your score as well.