Unique values in a list

for a one-time operation, it is best to use seeded Remove Duplicate function available through Data tab > Data Tools group on the menu ribbon.

for recurring need, you can utilise the following regular / non-array formula:

=IFERROR(INDEX(Sheet1!$A$1:$A$10,MATCH(0,INDEX(COUNTIF(Sheet2!$A$1:$A1,Sheet1!$A$1:$A$10),0),0)),"-")

if your data containing duplicate values are in Sheet1!A1:A10, and you want the unique values extracted on Sheet2, then, start on cell A2 in Sheet2 - either leave Sheet2!A1 blank or use a header value that is not a value expected to be found in your original data set on Sheet1!A1:A10.