What does SUMPRODUCT do in the following formula?

I am sorry for a noob question, but I am just learning.

Here there is a tutorial to find Last Occurrence of a value. SUMPRODUCT is used for arrays, but MAX in the formula below will return only one max value from an array:

=INDEX($B$2:$B$14,SUMPRODUCT(MAX(ROW($A$2:$A$14)*($D$3=$A$2:$A$14))-1))

and the tutorial's explanation is that

SUMPRODUCT is used to ensure that you don’t have to use Control + Shift + Enter, as SUMPRODUCT can handle array formulas.

I have no idea what Control + Shift + Enter does and what array formulas is it talking about. I have even removed SUMPRODUCT from the formula and it works. Would you please explain what the cited explanation means and why do we need SUMPRODUCT to use on a single number?