Summarize this article:

You will be prompted for a password. Example: sudo apt-get install telnet You will be promoted for that users password. Example: sudo bob telnet localhost 22 You will be promoted for a password. Type logout to switch back. You will be promoted for their password. Type logout to switch back.

Summary:
Type sudo before a command to execute the command as the root user. Type sudo <username> before a command to execute the command as another user on the system. Type su to switch your command line session to the root user. Type su <username> to switch your command line session to another user.