This command is essential if you ever want to have your own homepage. It
stands for 'change mode.' It is the command that allows you to change the
permissions (also called file access modes) on your files and directories.
What THAT means takes a little explaining. In unix, all files and
directories have permissions on them. These permissions are usually set so
that only the owner (the creator of them) can read, write, or execute
them. Permissions can be set, however, so that certain groups of others,
or everyone else in the world can read, write, or execute your files
and/or directories. IT IS NOT ADVISED THAT YOU SET YOUR PERMISSIONS SO
THAT OTHERS CAN WRITE TO YOUR DIRECTORY. 

To see the permissions of your files, you type:

% ls -l