An Example

Say you are assigned a Class C network number of 200.133.175.0. You want to utilize this network across multiple small groups within an organization. You can do this by subnetting that network with a subnet address.

We will break this network into 14 subnets of 14 nodes each. This will limit us to 196 nodes on the network instead of the 254 we would have without subnetting, but gives us the advantages of traffic isolation and security. To accomplish this, we need to use a subnet mask 4 bits long.
Recall that the default Class C subnet mask is 

255.255.255.0 (11111111.11111111.11111111.00000000 binary)
Extending this by 4 bits yields a mask of 
255.255.255.240 (11111111.11111111.11111111.11110000 binary)
This gives us 16 possible network numbers, 2 of which cannot be used:

Subnet bits Network Number Node Addresses Broadcast Address
0000 200.133.175.0 Reserved None
0001 200.133.175.16 .17 thru .30 200.133.175.31
0010 200.133.175.32 .33 thru .46 200.133.175.47
0011 200.133.175.48 .49 thru .62 200.133.175.63
0100 200.133.175.64 .65 thru .78 200.133.175.79
0101 200.133.175.80 .81 thru .94 200.133.175.95
0110 200.133.175.96 .97 thru .110 200.133.175.111
0111 200.133.175.112 .113 thru .126 200.133.175.127
1000 200.133.175.128 .129 thru .142 200.133.175.143
1001 200.133.175.144 .145 thru .158 200.133.175.159
1010 200.133.175.160 .161 thru .174 200.133.175.175
1011 200.133.175.176 .177 thru .190 200.133.175.191
1100 200.133.175.192 .193 thru .206 200.133.175.207
1101 200.133.175.208 .209 thru .222 200.133.175.223
1110 200.133.175.224 .225 thru .238 200.133.175.239
1111 200.133.175.240 Reserved None

 x

 x

 x

 x

 x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x