what I'm trying to do is copy a cell to a different cell based on date
(day),
A1 34 b1 todays date c1 copys only if todays say = 15th
I thought the formula woul look something like this
=if(today()=day(15),a1,"")
but that don't work.
is this possiable at all?

TODAY is a date and DAY(15) is an error. You need to apply the DAY function
to TODAY() and then see if that is 15...

=IF(DAY(TODAY())=15,A1,"")

Rick