Sure....

One of the typical uses of SUMPRODUCT is to multiply the corresponding cells
of 2 same-size ranges and aggregate the products.
Example:
=SUMPRODUCT(A1:A30,B1:B30)
would multiply A1 X B1, then A2 X B2, etc
then it would add up all of the results

In your case, we're tweaking one of those ranges (A1:A30) to substitute the
cell values with a boolean (TRUE/FALSE) expression.  When TRUE/FALSE values
are impacted by mathematical operators they convert to 1 and 0, respectively.
The math operator we're using is the dbl-minus-sign ( -- ). The
dbl-minus-sign is just a standard convention that we use to indicate that we
are converting a boolean (or numeric text) value to a number.

In this formula
C1: =SUMPRODUCT(--(YEAR(A1:A30)=2006),B1:B30)
This part: --(YEAR(A1:A30)=2006)
calculates the year for each date in A1:A30 and tests if it equals 2006.
TRUE values are converted to 1's,.
FALSE values are converted to 0's.

The end result is that each 2006 date becomes a 1 and is multiplied times
the corresponding amount in Col_B. The Non-2006 dates become 0's, so their
corrsponding values become 0's ( 0 x value = 0 )

The SUMPRODUCT function adds up the products (values from 2006 and zeros for
Non-2006 values)

Does that help?
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Regards,
Ron

XL2002, WinXP