This is a basic example of VLOOKUP in "exact match" mode. The lookup value is B6, the table is the range B5:C7, the column is 2, and the last argument, FALSE, forces VLOOKUP to do an exact match. (Read why this is necessary here).
If VLOOKUP finds a matching value, the associated cost will be retrieved from the 2nd column (column C). If no match is found, VLOOKUP will return the #N/A error.