Using different layouts (grouping)
There are 3 possible layout types in reports, each allows to take a different look at the data. Let's use an example.
Suppose we want to analyze time spend by team members on specific tasks. We create a new report and pick 3 columns: 'Member', 'Task', 'Reported Time'
When choosing 'Plain' layout type, there will be no grouping in the report. Data can be sorted by any column, but in fact, it will be just the entire list of records
When choosing 'With Subgroups' layout type, there is an option to specify by which column (or several columns) you want to group the data. I.e. on the left side of the report you'll see the information on the grouping and total on the numerical metrics used in the report. In our case, we group by 'Member' column, and the only numerical metric used in the report is 'Time'.
'Timesheet' layout is kind of 'Pivot' function in Excel. You choose 3 columns, two attributes (X, Y axis) and one metric. In our case, we analyze how much time a team member reported into a particular task.