IRAF is the Image Reduction and Analysis Facility, a general purpose software system for the reduction and analysis of astronomical data. The homepage for the IRAF project is http://iraf.noao.edu/iraf-homepage.html.
You may find "A User's Introduction To The IRAF Command Language" helpful.
To set up IRAF, decide on a directory where you will run IRAF, either from your home directory, or make a directory called iraf or something similar. cd to that directory, and set up the environment with the command 'mkiraf'. Choose xterm as your terminal type. This will create the login.cl file and the uparm directory. Then the command 'cl' will start IRAF.
NOTE: iraf (cl) must be run from an xterm window.
ALSO, before starting cl, the following command must be executed (this command can be added to your .cshrc or .bashrc file):
# for tcsh users (can be added to .cshrc):
limit stacksize unlimited
# for bash users (can be added to .bashrc):
ulimit -s unlimited