A protection stone (PS) is a sponge that, when placed, will create a 21x21x21 (10 blocks out from the center) protected area. Only the player who places the PS and players that are added to the PS are able to make changes to blocks and objects in the protected area.
Protection stones can be purchased at the Market located at /warp protect
/ps help - Lists all the commands for protection stones
/ps info - View information about the protected area you're standing in
/ps add <username> - Adds the username to the protected area you're standing in
/ps remove <username> - Removes the username from the protected area you're standing in