Companies require organization. This is pretty obvious, doesn't mater the size of the company, small or big they all want to be organized (most fail from my experience). You will rarely if ever see a company just have a single shared drive folder with the entire companies files dumped into one folder. There is a heirachy tree, there are sub folders based off locations, offices, teams, shifts etc. This type of organization is essential in networking as well especially for larger organizations, enter subnetting.
In the previous guide I had discussed the OSI model, and as mentioned in that guide Layer 3 (network layer) is one of if not the most popular layer for network engineers to work in. Subnetting can be a rather complicated concept at first, but it is very logical in its breakdown. IPv4 addresses are broken down down into 32 bit addresses. Look at 192.168.1.1, each of those numbers between periods is called an octet, each octet is broken into 8 bits per octet with each bit being 1s and 0s. Each bit represents a different number from 1 to 128, because of this the highest possible number of an octet is 255. Subnet masks for a particular IP address denote the the size of a subnetwork. For example, 192.168.1.0 255.255.255.0. The second IP is the subnet mask, if you broke the octets down into bits it would be 11111111.11111111.11111111.00000000. Each of those 1s is a network bit and 0 is a host bit. When two networks sit on the same subnet they share the exact same subnet mask. For example, a computer with an IP of 192.168.1.10 255.255.255.0 cannot talk to a computer with an IP of 192.168.2.10 255.255.255.0. This is because the 1 and 2 in the 3rd octet lies in the network bit range. if you broke there 3rd octet into bits you would get 00000010 and 00000001. The only way to put the two in the same subnetwork is either to change there IP addresses or expand the subnet.
Consider the below IP addresses. I went ahead and entered a pipe to make it easier. The subnet masks 3rd octet is where the 1s end. Note that the network bits end 3rd from the right which adds the bits up to 248. This means the 2 IPs 192.168.8.0 and 192.168.64.0 are seperate networks. Now consider the green row, the .10 network broken down into bits has the same network bits as the .8 look at just the bits to the left of the pipe and they are the exact same this means that the 192.168.8.0 and 192.168.10.0 both with the subnet mask of 255255.248.0 are part of the same subnetwork.
I understand this is still probably kind of confusing, trust me I'm trying best to not throw too much at you, but its easiest if you get some practice. This is just the first part of subnetting, next time I will go into broadcast and network addresses along with possibly public and private IPs.