Subnetting is a process in which the network administrator further divides the host part of an IP address into further smaller ‘subnets’.
The subnet refers to the group of devices, which all share an address that associates it with other devices in this group.
The IP address is used to identify a device on the network. With subnetting, the host part of the address is divided into two or more subnets, with part of the host address identifying the subnet.
Potential advantages of subnetting include more efficient allocation of address space and improved routing efficiency. It also allows different administrators to manage subnetworks within a larger organisation.
A practical example might be configuring different groups of printers for use by different departments within an organisation.
Subnetting could be used so that one department sees one set of printers and the other department sees the other set.
There is advice available online on how to configure subnets, with a basic understanding of concepts such as binary required.