What do the logical operators AND, OR, XOR and NOT do?

AND (both conditions on either side of the AND operation MUST be satisfied for the IF function to work)
OR (either condition on each side of the OR operation MUST be satisfied for the IF function to work)
NOT (used when something needs to be displayed UNLESS a value is a certain amount/type/name etc.)
XOR (used when exclusively ONE of the conditions has to be met – not both! This is where XOR and OR differ.)