I don't understand the difference between these terms and how they are connected.
I looked at a hosts file on my computer and could see that 127.0.0.1 and localhost are connected but not sure how and I don't know where 0.0.0.0 fits into all this.
I've seen other answers to this question but I'm a newbie and the other answers about loopbacks and meta-addresses weren't easy to follow.
Yes, on your local system localhost does translate into 127.0.0.1, which will always be the IP address of the machine that you are currently using. For example, on your computer accessing 127.0.0.1 (or localhost) will just attempt to open a connection with your own computer (useful if you're hosting a local web server)
Meanwhile, 0.0.0.0 has a different use. On a server or any machine with more than 1 ip address, it can be used to refer to all of the IP addresses that the machine uses. For example, if you create a simple java application with a serverSocket, you may want the server socket to listen for incoming connections on all of the servers IP addresses. You would then set the server socket to listen on 0.0.0.0. Hope this helps!