Because #56# is an even number we can factor it by #2# giving:
#56 = 2 xx 28#
#28# is also even so we can again factor it by #2# giving:
#56 = 2 x 2 x 14#
#14# is also even, so again, we can factor out #2#, again.
#56 = 2 xx 2 xx 2 xx 7#
#7# is a prime number so our factoring is complete.