The dollar sign
$ at the command prompt means that you are logged in as a "regular / normal" user (you don't need to type the dollar sign). The pound symbol
# at the prompt means that you are logged in as the "super user / root".
When you first open up the console it might look like this:
When you are going to log in as the "super user" or root you type:
After you enter your password, the console command prompt should look like this:
The space and dash (or hyphen)
- after
su logs you in as the "super user" with root's environment and paths (privileges and functionality).
Make sure that you type
exit or
logout at the prompt, to return to normal user mode.
Be careful, you should sign on as root only when carrying out activities that require root access.
Edit: RHELL, you beat me to it!