Read /usr/doc/Linux-HOWTOs/Bash-Prompt-HOWTO. If you didn't install the HOWTO's, go to
http://www.linux.org/docs/ldp/howto/...EX/howtos.html
They are all there. Briefly, you need to set the PS1 environment variable in your .bashrc file. For example the following line appears in mine:
PS1='[\u@\h]:\w\r\n#'
This results in a prompt that looks like this:
[musrum@tux02]:/usr/doc/Linux-HOWTOs
#
That is [username@hostname]:currentdirectory. I add a crlf to the end of my prompt so that I always have the full terminal width to type commands on, and my commands always start at column 1.