SELECTEDVALUE(Column, Alternate) returns the value of a column when exactly one value is left in the filter context, and the alternate result when there are none or several. In a row for West, SELECTEDVALUE(Store[Region]) is "West"; in the Total row it returns the alternate.
That makes labels that follow the report: "Sales for " & SELECTEDVALUE(Store[Region], "all regions"). Put a text measure like that in a card or a title.
HASONEVALUE(Column) returns TRUE when one value is left. Wrap a measure in IF(HASONEVALUE(...), ...) to leave the Total row blank when a total makes no sense.
ISFILTERED(Column) tells you whether the column has a filter at all, from a slicer, a row or the Filters pane. Remember the edge case: several values selected in a slicer isn't the same as one.