Hello, new to spreadsheets, please help.

I try to create my familly budget.
I have this ( snippet ) sheet with this named columns:

DataDebit ( type date, formated YYYY-MM-DD ), Debit ( type currency, with BGN format )

Example values:
2006-08-01, 100
2006-08-20, 110
2006-09-01, 300

Problem: I want to get in another cell the sum of Debit-s ONLY for August records. Tried with SUMIF,
my primary idea was to define the dates as interval, as I often do when I program on Perl for example:
x >= 2006-08-01 AND x <= 2006-08-31, but do not know how to do it here. Here is what I tried:

=SUMIF( DataDebit; ">=2006-08-01"; Debit )

IN FACT I would like to know how to do it both for SUM of the whole Year, and separate calculation for only August.

Been looking in the help index for date/time functions such as month( date ) or similar but there are none.
Been thinking of using RegEx, but not sure if this is the way...

Any ideas please?