IP addresses are split into public and private ranges to conserve addresses and improve security.
Private IP Address
Used inside your LAN. It is not routable on the internet. Common ranges are 192.168.x.x or 10.x.x.x.
Public IP Address
Assigned by your ISP to your router. This is the address the internet sees. Your router uses NAT (Network Address Translation) to translate between your private devices and the single public IP.