A network is defined by its network address, its subnet mask and its broadcast address.
The network address is the lowest possible address in the network, and it's reserved with the meaning "the network itself, no specific host on it". This is not used for actual communications, but it's important for routing tables. It can't be assigned to a host.
The broadcast address is the highest possible address in the network, and it's reserved with the meaning "all hosts on the network". This also can't be assigned to a host, but unlike the network address, it's actually used for communications, because some protocols need to be able to send messages to all hosts on a network (NetBIOS anyone?).
Network address: 192.168.0.0
Subnet mask: 255.255.255.0
Broadcast address: 192.168.0.255
Usable addresses: from 192.168.0.1 to 192.168.0.254
More complex example:
Network address: 172.16.2.32
Subnet mask: 255.255.255.224
Broadcast address: 172.16.2.63
Usable addresses: from 172.16.2.33 to 172.16.2.62
The network and broadcast addresses are given you for reference, but you don't need to configure them anywhere; both of them can be (and are) computed automatically, given a host's IP address and subnet mask.
All the info you want and many more here: How does Subnetting Work?.