Most of these commands are the basic need-too-know things for a Minecraft User.
/msg, /m, /tell, /whisper <playername> <message>: Allows you to speak to a specific person, and only they will see it.
/r <message>: Will reply to the last player to send you a private message.
These are basically used when either reporting grief, asking to buy Spawners, Warps etc.
/pe open <message>
Example: /pe open I would like a grief check here. - Make sure you type this standing at the point that was griefed.
/pe list - Lists all of your open petitions
/pe close <number>
/pe view <number> - Do this is you want to read any comments from staff or if petition if it's closed.
These commands allow you to teleport to certain locations.
/sethome <homename>: Sets the target of the /home command where you are standing. (maximum of 2).
/delhome <homename>: Removes a previously set home.
/home: Lists your homes that have been set.
/home <homename>: Warps to your home.
/warp: List's all of the available Warps.
/warp <warpname>: Teleports you to the warp you enter.
/spawn: Teleports you to the server's spawn.
/f home: Teleports you to your faction's home.
Tired of people breaking into your house? Well these commands are good for you!
/cprivate: First of all, type the command into your chatbox, and press enter. Next, left click the item you want to lock (Door, Trapdoor etc). After doing that, only you can open that mechanism.
/cpassword <password>: Lock your mechanism with a password. Anyone that knows the password will be able to open it.
/cremove: This command is used to remove a protection that you placed on a mechanism.
/cinfo: Type this command, then left click the protected object, and it will show you who placed it, what type of lock it has, and if you can access it.