currency swap

wanted to know the difference between currency SWAPS and interest rate SWAPS

,now what i know in interest rates SWAPS we get the difference of the differences when we have fixed and Floating rates for both parties

while in currency options we add the differences being between each party’s country of one country’s fied rates and other country’s Variable rates

however there’s a question in BPP textbook on page 294 illustration 7 currency swaps they took difference of differences

iam little confused in this area