This plugin does nothing by its own, but serves as provider of awesome chart.js library, which can then be reused in other. It allows you to easily use js-rendered charts to the job page or to the view page.
See examples of known plugin consumers for:
This api is simply adding the chart.js library to the view and/or project page see header. You have to first require it in your pom.xml:
<dependency>
<groupId>io.jenkins.plugins</groupId>
<artifactId>chartjs-api</artifactId>
<version>${chartjs.version}</version>
</dependency>
And then, e.g., in your column.jelly or floatingBox.jelly you can use powers of chart.js directly. See appropriate files in the above projects for examples. See https://www.chartjs.org/docs/latest/, and you should be ok to script it in without issues.