What are minecraft permissions in Bukkit?

How do they relate to plugins, and do I need to use permissions? I'm a newbie and have no idea what permissions are used for. I have a permissions file but when I open it with Notepad ++ it doesn't have anything in it (it's blank)

Permissions allow you to specify which groups of players are allowed to use which commands. Https://github.com/PEXPlugins/PermissionsEx/wiki

GroupManager is much easier in my opinion. I have never used PEX although I did try it once. I had a hard time since when I opened it with Notepad++ it was emptied as well. But for groupmanager when you open it, it gives you an example. The examples were Default, Builder, Mod, Admin, Owner. With there specific permissions. (Not all have) You can go to google and type in Essentials Command Reference. Certain plugins have certain permissions. For an example worldedit. The node would be worldedit.* if you want to give that rank all the worldedit commands. Then you save it and go ingame into your server and set your rank as for an example builder. Then you try using worldedit and it works! Make sure not to put worldedit into the inheritance section, but into the permissions section, make sure it's all lined up or you will have a manload error. Sorry for the long answer:3

Hope I helped,
V