The standard shell on Helix is bash. Under bash when you log in, the operating system creates a login shell for you. This shell looks in your home directory for your .bash_profile file and follows the instructions it finds in this file.
Another startup file .bashrc is only for interactive non-login shells (such as when start another shell, or get allocated nodes on the Biowulf cluster).
When you logout, the file .bash_logout is interpreted.
You can list your startup files using the command ls -a.
Some examples of defaults you can set in your .bash_profile file:
Setting your default printer. Your .bash_profile file should say (with [printer] replaced with your default printer):export PRINTER=[printer]
Setting your path:PATH=$PATH:$HOME/bin
Another shell is csh, and its fancy derivative tcsh. Under csh, .cshrc is first interpreted (under tcsh, the OS will look for .tcshrc first, then .cshrc). The OS will then look for .login. Upon logging out, it will look for .logout.
The same commands above in bash are translated to tcsh/csh and would be placed in .cshrc:
Setting your default printer:setenv PRINTER [printer]
Setting your path:set PATH = ( $PATH $HOME/bin )
Other shells available are sh, ksh, and zsh. See here for more information.