P-value in Excel

Hi all,

I am currently doing a scientific research study and decided to compile
my data for statistical analysis in Microsoft Excel.

I know that to calculate my p-value, I have to type in the formula box:
=tdist(abs(x10),18,2)

which gives me the correct p-value... But I don't understand why! I
know it shouldn't really be bugging me, but I would rather know why
the formula works. Could anybody explain why this formula would give me
the p-value? Thanks in advance.


Cheers

.