What are 127.0.0.1 and localhost?

they are the same thing. The computer the OS is running on, your computer.

'localhost' refers to the computer that you are currently using. This is given a local private IP address of 127.0.0.1. You can use this IP address to access a server on the computer from another program running on the same computer, without knowing any specific IP address that is assigned to the computer over an external (to the computer) network. For example, the computer might have an address on its Ethernet connection of 192.168.0.123. If you have an HTTP server running a web site on that computer, from a browser running on that computer, you can use either IP address. However, from a browser on a different computer, 127.0.0.1 will not work as this would be attempting to access a service on that different computer.

Unlike other addresses the computer might have for external interfaces, 127.0.0.1 will work even if the computer has no network adapters installed.

I hope this helps.