Data > Remove Duplicates deletes rows that repeat an earlier row and keeps the first one. In the dialog you tick the columns that must match for two rows to count as duplicates:
- all columns: only rows that are identical everywhere go;
- some columns: rows that match on those go, even if other columns differ. Ticking only Email keeps one row per email address.
The comparison ignores capitals, so "Ana@x.example" and "ana@x.example" match. Excel tells you how many duplicates it removed and how many unique rows remain. The rows below the list move up; the deleted rows can't be found again except with Ctrl+Z, so work on a copy when in doubt. For a list that updates by itself, use =UNIQUE() instead.