If you are not familiar with DHCP (and the other networking processes involved) then you will probably have a difficult time getting these to work properly. I'll try to explain as best I can.
In a network each device needs an IP address so that they can communicate. Routers typically use DHCP (Dynamic Host Configuration Protocol) to assign IPs to the devices automatically.
You router has two IPs, a public IP and a private IP. The public IP is the IP that is assigned by your ISP. The private IP is the IP used by your router to communicate to the computers on your internal LAN. It assignes private IPs to these devices. Devices need to be on the same network (determined by part of the IP address) in order to communicate with each other. To communicate with PCs on a network a router is needed in order to bridge the two.
Your private IPs probably start 192.168.0.xxx or 192.168.1.xxx. If youchange that third number then they are different networks.
When you click a link for a web page on your PC, the request is sent with your PC's private IP address to the router. The router then converts the request to have it's public IP address and sends it on to the web server. The web server then sends the response back to your router, which then redirects the response to your PC's IP address.
If you connect a 2nd router to the first, the 2nd router will get an IP from the 1st router and consider this it's public IP. It will then create a new internal network for itself and the connected devices.
Now, I don't know if a router can have public and private IPs that are on the same network. Actually I would be surprised if they could. But, if so, you would then have to make sure that the IP's assigned by the second router do not duplicate the IPs assigned by the 1st.
If you are only connecting one computer to the second router you can put that computer in the DMZ (too long to explain). But that won't work if you have 2 or more connecting to that router.