How to discover a router's ip in lan?

Hello guys, I'm absolute noob in networks.

So, there's a second router which I want to use as a wi-fi access point, so I want to configure it somehow.

layout: isp -> first router -> switch -> other stuff

-> 2 router (wi-fi acces point)

What I need to do to get into router settings?

And can you suggest some books/guides about networks, please, because I'm feeling ashamed to ask questions like this.

Thanks in advance.

To log in to the 1st router, you need the IP of the 1st router, and it's password. The IP usually is the same asw yours, except replacing your last 3 digits with the number '1' Your isp can usually help, since doing that saves a service call.

Post the make and model of your 2nd router. Does it still contain the original firmware?

The typical home router has the default password on the tag on the bottom of the unit. If it has been changed and you do not know the password then you would need to reset the unit.

All you need to do is connect the cable to one of the router's LAN port to a computer isolated from your main network. By default the computer should be configured by DHCP so the gateway address is the IP address of the router.

Login to the router and turn off the DHCP server.
Set the wireless settings and password as desired.

Set the 2nd router's LAN IP address to match your home LAN subnet with an address outside of the range of your first router's DHCP range. Once set you will lose connection to the router. You should be able to then plug the switch into a LAN port of the 2nd router and be able to connect using its wifi.

Okay, I know how to get into settings of my 1 router, but I want to configure my 2 router to be an wi-fi access point, currently it works as a wi-fi access point, but
1)It doesn't have password
2)It works like an separate wi-fi point, can it just be a part of 1 router's "wi-fi network"?

So, that's why I need configure it.

Well, Router 2 sounds like a a wireless extension point. Your router 1 should show you who is connected, and what the IP is. But if it all works, why fix it?

It works like an separate wi-fi point, can it just be a part of 1 router's "wi-fi network"?

It does sound like a wifi extender. Please post the make and model number of this device.