When you are trying to solve a formula like this one, you need to consider the whole row in the spreadsheet, not just A1 and D1.
So, A1:D1 refers to the whole row, which means that you need to add A1+B1+C1+D1 = 2 + 1 + 5 + 3 = 11.
The answer to the formula according to this spreadsheet is 11.