Sample is nothing but it is capturing or sampling the values on the I/O's.
if there are two chiops on a board lets say A and B .
Now A chip's has 2 I/O's lets say . and B chip has 2 I/O's lets say.
Now the values of the I/O's on the A chip are captured in to the B chip this is nothing but sampling.
Now you need to load the I/O's with some known values on the A this is nothing but Preload.