To access(log into) the router and/or modem-router use your browser and Internet Explorer seems to be more reliable.  Enter the Default Gateway number (LAN TCP/IP Setup) in the browser  upper left window.  The one that normally has things like amazon.com 
There are a number of different default gateway numbers that are used but the most common is:  192.168.1.1   192.168.0.1 is also used. 
If that code does not work, then you can see what it really is by entering "cmd" in the search window then tapping on cmd.exe when it pops up to bring up the command prompt.

Then enter "ipconfig"

It will tell you a number of things, one of which is the "Default gateway"  That is the number you want.

If you are asked for a user name and password, the typical default User name is "admin"  the typical default password is: "password".  Normally I would not use the default password but this is an exception.  The only people who can be in a place to access your router has to already be on your network so they have had to enter the password to get to that spot.  Also there is little mischief they could cause by getting in.
This is unrelated to the password you use to get on the network wirelessly.

Setting up a DSL network

You will need a user name and password from the phone company.  It should be with the original paper work but if you have misplaced it, then just call them back.  If you ever reset or replace your modem, you will have to reenter this information.

At times there are other things that need to be configured so you may still have to call them.

Setting up a user defined network name (SSID) and password so others can use the WI-FI features.

You may also want to enter these settings if the network name and password are not convenient.  Often the company supplied user name is not obviously associated with you and the password is a LONG string of nonsense characters.

To get access to your router settings, enter 192.168.1.1 or its equivalent in your browser than look for spot to enter wireless settings.  Here enter the desired Network Name (Name or SSID). This is what shows up when one is searching for networks nearby.
http://192.168.1.254/ is another common number.

Then enter the the security option you want, typically the one that has WPA2 in the title.
The final thing is the password (passphrase) which must be at least 8 characters long with no  blanks.

Setting up a second WI-FI hotspot with a second wireless router.

The trick is you need to change the IP address in one of the routers.  (Do it when the other router is not connected to the network or it may get changed also.) To do this log into the router as described above. For my Netgear router, I clicked Advanced then Setup then LAN Setup.  at this point you can change the IP Address.  It was under LAN TCP/IP Setup.  You should not change the IP Subnet Mask number.  For example, on my system I changed the IP address from 192.168.1.1 to 192.168.10.1
You must use an IP address that is not already used elsewhere in the network.  To see what is being used, go into you router as described above and look for a menu item like "Attached Devices".  You will then need to run an Ethernet wire from the first router to the second one.  Connect it to single input Ethernet port.
Apparently you can also connect it to a regular port in with case the new router will act as if it was just part of the original one meaning that the users would have complete access to any shared files and you probably would not have to change the IP addresses.