|What do you mean by "sum of each month pertaining to the dates"?|
Do you have another column of values that you are trying to sum based on which month those values correspond to?
If so, this Array formula should do it, with the 1 pertaining to January:
=SUM(IF(MONTH(A1:A5)=1,B1:B5,0)) Entered via Ctrl-Shift-Enter
as will this non-array formula:
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