It really depends on how your data is laid out and what you want to compare.
If I'm trying to find out if a single cell's value is in column A of a different
sheet, I'd use a formula in an adjacent cell:
=isnumber(match(a1,sheet2!a:a,0))
It'll return True if it's there, false if it's missing.
If I wanted to check the value of two cells in the same row against two columns
in the other sheet, I'd create a new column on both sheets that joins the
columns together and then use the =isnumber(match()) formula:
I'd insert a new column and use a formula like:
=b1&"--"&c1
and drag down
