The permission to do something is a major component of hacking. Often, we are trying to escelate our privligae in whatever scenario that is. This can mean becoming the admin of a computer you don't own, or simply being able to access restricted things in a video game. Following in this nature, files in the Linux operating system have permissions.
To learn how they work, read this. It should be easier and faster than the earlier sections, considering you may have already encountered permissions in your own system.