It essentially ignores column C's missing entry and only considers the other two. ( Although the fourth criterion in your example formula is not obvious from your list, the procedure can be expanded to include as many criteria as you may have.
To make things easier to comprehend, I made a named range Lists that includes your sample range E2:H10 and labelled I2:I10 as SumRange. The first column in the range is shown by INDEX(Lists,,1). It's crucial that Lists and SumRange both include the same amount of rows.