Where does one find out in detail about this and other Excel functions
outside Excels own help

for example, I often see formulas such as

=SUMPRODUCT(--(A1:A10=B1:B10),(C1:C10))

quoted, and one guy helped me out with this on a sheet of mine, but I have
no idea where the two "-" signs came from, how they work or how you find out
about these. Is this array arithmetic? If so, where is that detailed in the
help, or on the web?

thanks in advance
LH