Grouping turns individual dates or amounts into reporting categories. With a Date field in Rows, Group Selection can produce months, quarters or years. Numeric grouping uses a starting value and an interval, such as quantities from 0 through 4, then 5 through 9. Check the boundary values before you interpret the totals.
A label filter tests the category text. A value filter tests that category's aggregated result. Top 10 is a value filter too; you can change the item count, and ties at the cutoff can include more than that count.
A slicer makes a field's allowed items visible as a set of choices. It filters the same source records as the report, so two filters combine rather than replacing one another. Clear an old filter before changing the report's question.