Router IP address allows network admin to login the router management page to configure settings such as change WiFi passwords and SSID, create guest users and so on.
Router brands such as TP-Link, D-Link, NETGEAR mainly uses 192.168.1.1 and 192.168.0.1 as their IP address however that may vary from users so you may want to read how to find your router IP address to be able to determine the correct IP address before proceeding.
Here is a list of all the default router IP addresses. Simply select an IP address and you will be taken to user guidelines.