We have talked our way up from pushing the power button to the point where an instance of getty provides you with a login prompt, so now what happens.

When you provide your username and password, if you're authenticated, then you are provided with a bash prompt. Without you knowing, bash looked at a series of files for it's configuration. The first of these are the system-wide configuration files /etc/profile and /etc/bashrc. /etc/profile is usually used for system-wide environment variable setup such as your PATH, etc. /etc/bashrc is usually used to execute scripts upon startup, setting a default prompt, setting up command aliases, etc.

Next bash looks in your home directory at the files .bash_rc and .bash_profile. These files serve much the same purpose as the previously mentioned files, except they only apply to you personally.