# Basic syntax:
=COUNTIFS(A:A,">="&EOMONTH(TODAY(),-1)+1, A:A,"<"&EOMONTH(TODAY(),0)+1)
# Where:
# - countifs counts cells in column A that meet multiple conditions,
# here, it counts cells that have a date between the first and last
# days of this month
# - countifs requires conditions to be passed as strings
# - EOMONTH(TODAY(),-1) is the last day of the previous month. Adding
# +1 sets it to the first day of this month