Report show total if value from field code changes

Hello together,

I would like to create a total, if the value from the field "Code" changes like this:

thing:1, code:1, amount:1
thing:2, code:1, amount:3
Total Amount: 4

thing:3, code:2, amount:2
thing:4, code:2, amount:1
Total Amount 3

Somebody wants to help me? i know it's a very basic question... but i could not find it out..