In the repository, you can share collections. Collection is defined as a set of resources that belongs together i.e can be used to create a coherent map design or to do a specific task.

The items that you can share on the repository are:

Item Notes
Images SVG files or other image files that can be used for svg marker or raster fill
Symbols In the form of XML that could contain marker, line, fill, or colorramp
Styles In the form of QML file
Processing scripts Python processing scripts

Note that you can actually put other QGIS resources in the repository (composer templates or project files), but for now they will be ignored in a way that the plugin will not do anything to them (e.g installing the resources).