Assuming you want to count the values from another column according to date values >=$C$6
and <=$C$8
, you could adapt an example from the Conditional Counting and Summation HowTo. It's based on the SUMPRODUCT function.
=SUMPRODUCT($N$16:$N$9000 >= $C$6; $N$16:$N$9000 <= $C$8; $P$16:$P$900)
(assuming that P16:P9000
holds the values to sum up)