Click on the icon "Group". Below the column headers you can see an area titled "drag columns here for grouping."

Drag with the mouse one or more columns and drop them into this area. The view will be shown grouped by this column.

Click on a small +/- icon in each row to expand or collapse the group.

Click on the + or - icon in the toolbar to expand or collapse all groups.

Click again on the icon "Group" to return to the default view.

Some useful groupings are already prepered. Click on the small arrow next to the icon "Group" and select one of these Preferences.