Can someone please explain this to me?
auser:x:500:500:Anne User:/home/auser:/bin/sh
buser:x:501:501:Bob User:/home/buser:/bin/bash
I'm used to it looking like this. What is the difference between the first name and second name? In the first case I had to use the first name to change my password.
auser:x:500:500:auser:/home/auser:/bin/sh
buser:x:501:501:buser:/home/buser:/bin/bash
The first field is the username. The fifth field amounts to a title, and isn't really used that much. Some UNIX systems occasionally use it for special purposes.
The username is supposed to be all lowercase letters, digits, or underscores, no spaces or anything else, so a more descriptive name to attach to a user can be useful sometimes.
On my Fedora system it allowed me to use uppercase letters. Is that a problem? My professor said that was a bad so I deleted that user and changed it to lowercase.
Here's a trick: Switch to a real terminal (ctrl-alt-f1 through ctrl-alt-f6, ctrl-alt-f7 or f8 gets you back to GUI), and login to a lowercase user in ALLCAPS.
Unless they ripped that out by now, it'll let you do it, and even switch to a special translation mode with no lowercase characters. It's a compatibility mode for really old terminals.
Some things may depend on usernames being all lowercase. Others might not. Best not to tempt fate.