Where to set aggregation to get group settings
Grouping is available for sorts and filters. To use grouping, “Use grouping” must be enabled on a per-view basis in the Views UI. This is toggled in the Advanced settings box by clicking the link next to “Use grouping”. Once you activate this checkbox (be sure to read the notes in the UI!), functions for aggregating particular fields will become available. The gear icon that should be familiar to users with any amount of Views experience will now appear next to any sorted or filtered field with aggregation capabilities. Choosing that icon will open up the configuration for the aggregation functions. As an example, this could be used to count things like number of posts in a day, or number of published posts. This could also be used to sum the values of a row, instead of everything in the view.
Setting only the "Use aggregation" turned on itself does nothing. It only gives the possibility to set Aggregation types.
Different aggregation possibilities
It should be noted that modules that are providing data to Views are responsible for noting whether a field supports aggregation or not; modules that do not provide this information may not have all of their fields available to Views if this data is not in place.