To report on groups, simply navigate to the Reports> All Built-in Reports > Groups page.
From here, you will find a range of reports related to your groups, including reports on the people within your groups, group attendance and group reporting.
Clicking on any of these reports allows you to customize the reports further. For example, you may be able to report on a particular date range, or filter by particular locations, service types, departments and demographics. In some reports you are also able to display results as a graph.