To plot something on the map, click the parameters icon () next to the "chloropleth" column on the bottom right, edit the expression and click save. If your data isn't in the range 0-1, you should add "quantiles" to the search parameters of this page (e.g. like this). If you're stuck watch the short video tutorial on GitHub where you'll also find the source code.

Documentation for each column is available in French on the INSEE website. I've added an "area_km2" column for density calculations.