Now that you know what permissions are, you probably want to know how to change them, because listing them can only get you so far. Listing them will help you to get a good grip on what is there, but to make changes you need to take the next step, which is to use the chmod command. There are two modes of operation that you can use with chmod: a quick-and-dirty mode, and a more user-friendly way of setting permissions.
The user-friendly mode uses easy-to-remember commands to set or unset permissions. To use this, do the following:
Pick a permission level. If you want to set permissions for the owner, the level is u. If you want to change permissions for the group, it is g. For other permissions, choose o. Lastly, if you want to ...