Okay, at this point we have a user login. At the login: prompt, we want to type in our user ID. If we enter a login ID which contains NO lowercase letters, almost all UNIX machines will assume you are trying to login from an ancient teletype which only has uppercase characters. And it will translate ALL alphabetic characters to lowercase. This is probably not what you want to do. For instance, some commands have both uppercase and lowercase options; and usually they behave very differently.
After you type in your login ID and hit the Enter or Return key, the system will respond with a prompt for your password. Type it in, and if you have entered a valid login ID and password, you will be rewarded with a command prompt from your login shell. The prompt is easily customizable, so I am not going to try to duplicate a prompt here.