Each time you login to a UNIX host, the system looks in your home directory for initialisation files. Information in these files is used to set up your working environment. The C and TC shells uses two files called .login and .cshrc (note that both file names begin with a dot).
At login the C shell first reads .cshrc followed by .login
.login is to set conditions which will apply to the whole session and to perform actions that are relevant only at login.
.cshrc is used to set conditions and perform actions specific to the shell and to each invocation of it.
The guidelines are to set ENVIRONMENT variables in the .login file and SHELL variables in the .cshrc file.
WARNING: NEVER put commands that run graphical displays (e.g. a web browser) in your .cshrc or .login file.