VLOOKUP() is the way to go:

In A1 (or wherever you begin), =VLOOKUP(B1,$C$1:$D$3,2,FALSE)

Explained:

B1 is the value you're looking for;

$C$1:$D$3 is the range in which you will be looking and returning from, note that VLOOKUP will always search in the first column (so C column); Adjust according to your actual range; Now I've used absolute references, so you can just drag down from here on.

2 is the column number which you wish to return (so D column);

Wrap the thing in ISERROR(formula here, "error message here") to add an error message if not found:

(Column A contains the formula, column B was manual input)

XLOOKUP() would make this easier, but I don't think that works in Excel-2010.

Edit: added FALSE argument to the formula to find only exact matches, thanks Darren Bartrup-Cook