Under the Map tab are a range of tools to generate and style web maps of spatial data in GeoPackage files using Leaflet.
In the side bar, Select active layer presents a dropdown list of layers that you can render on the map. If you try to select a non-spatial layer you will get a warning.
Select variable is a dropdown list of columns associated with the selected layer, the values of this column will be mapped to a colour palette when visualising features on the map.
There are a range of other map styling options such as picking the Fill colour palette (refer to this reference for useful advice on choosing colour palettes), Opacity of features, Line width, and whether to display a legend.
You can scroll down the sidebar to find more options such as whether to display a legend and to create a legend title.
At the bottom of the side bar is a widget where you can select one or more columns from the layer to generate popup labels. When you click on a feature on the map, that feature’s values for the selected columns will appear as a popup.