I am trying to use a Vlookup to look up the left most field of a table, in
another worksheet and return the match of the column heading. I am not
getting results, just the formula itself. From everything I've read here it
is because of a data mistmatch but I cannot seem to be able to fix it even
though I sinked up all of the data types and retyped the formulas.

Does anyone know a way to fix this?
What does the last zero mean in the vlookup/match formula below?

VLOOKUP("Single",$A$1:$D$4,MATCH("Termo",$A$1:$D$1 ,0),0)

Thanks for your help in advance.