192.168.1.100 is a Ipv4 and private IP address used by many local networks. The start of the dynamic range of your home network typically will begin with the IP address of 192.168.1.100. This IP address is important when you are setting up your computer network.
Typically the first device or computer you add to your network will be automatically assigned the 192.168.1.100 address by the Dynamic Host Configuration Protocol (DHCP). However, you do have the choice to change the range of the router in the settings to either use the automatic 192.168.1.100, or not.
If you decide to use the default settings and have 192.168.1.100 to be assigned first, your other devices or computers will correspond to that IP address. The second device or computer connected to your network will receive the IP address of 192.168.1.101. The next device and computer connected will be assigned 192.168.1.102 and so on. Using the default Dynamic Host Configuration Protocol will give your devices and computers individual discrete IP addresses on your network every time you connect one to your network.
192.168.1.100 can not be accessed through the Internet. If a computer is assigned this IP address and wants to connect to the Internet, it will have to be redirected though either a router or another computer.