When a visual has a hierarchy, you can drill down to reveal additional details. The user will know this is available upon seeing more icons associated with that visual, represented by several arrows pointing up and down. The level in which the user can drill down and up is predefined when the report is developed.
In order to drill down on a specific field of a visual, the Drill Down icon must be toggled. This will allow the end user to select any field and rather than triggering a filter, the visual will drill down to show expanded information.
For example, if a visual shows a 6 month view, toggle the drill down icon and select the data associated with a month, like August, to see the daily data for that month.
This function allows the user to drill up and down all available hierarchy levels, not specific to a field. The above images shows the difference between two levels.
Expanding all fields is very similar to Drill Down one Field at a time, except the visual will take every available field and expand it across the entire visual.
For example, if a visual shows a 6 month view, the user can drill down one field at a time by selecting a month - therefore showing all details in that month. Expanding all fields will have the same breakdown, but across all 6 months.