=SUMPRODUCT(--(Sheet1!$B$2:$B$5=Sheet1!$C11),--(Sheet1!$C$2:$C$5=E$2),Sheet1!$G$2:$G$5)

What does the "- -" mean in the formula above? This is a new formula for me
and want to be sure I fully understand how it works... the "- -" is the only
part throwing me off.

thanks for your help on this.
take care, Jane