Command Reference/Perm
From Essentials
Essentials is made up of multiple components, you must place each jar that you intend to use in your Minecraft/Bukkit plugins folder. You will generally not need/want all components, ignore the commands & permissions from the modules you haven't installed.
If you aren't sure what each component does, first check the breakdown page
Permissions aren't automatically inclusive, you will need to give both 'essentials.spawnmob' and either 'essentials.spawnmob.wolf' or 'essentials.spawnmob.*' to allow use of "/spawnmob wolf".
Example Permissions
There are a number of example permissions files available for GroupManager:
Group Manager Groups :: Group Manager GlobalGroups