This command has several uses.
cat .cshrcto display your .cshrc file on the screen. To list any other file, repeat the command, but replace .cshrc with the name of the file.
cat > junk(If you already have a file called junk you should use a different name.) Then type anything. For example
This is 100% pure unadulterated junk.Type another line, if you want. Then end the file. To do this you must type a Ctrl-d. That is, hold down the Ctrl key while hitting the d key. That is the keyboard end-of-file signal.
Now type ls in the window. You should see the file junk that you just created. Then type cat junk to display the file. It should be exactly as you created it.