purpose of broadcast and network id ?

hi, let say i have been given an ip address where i need to do sub-netting. ex:
x.x.x.x /28. after doing the sub-netting i would end up with the ‘Network ID’, range of IP that can be used and the ‘Broadcast ID’.
So, the range of ip’s i know that is for the hosts..printers, computers ..etc. where do i use the broadcast and network id? What is for exactly?
can someone help me please. Thanks in advance.

ex:
network id range broadcast id
x.x.x.16 17-30 x.x.x.31