To access your router, you need to connect to the IP address of the device.  In most cases, your login will be the default username and password created by the manufacturer. 

The IP addressing scheme is determined by the company that provides the service. 

Comcast usually uses: or
Many others use: or


Most manufacturers have a default login of

admin / admin


admin / password


When you login, some devices force a password change.  So you might try:

admin / lockdown77

admin / Lockdown77