On my worksheet, cells A1 through to B6, I have the values 1,2,3,4,5,6 from A1, A2, A3, etc.
In cell D1, I type:
=SUM(A1:A3*B1:B3)
and enter it as an ARRAY formula to get the result of:
32
I understand how this is arrived. It is multiplying cell A1 with B1, then A2 with B2 and then...