This item will give you one use of the /berserker command - it allows you to put the Berserker ability on battleaxes and warhammers. You can buy multiple uses for multiple items.
To give your weapon the ability, simply hold it in your hand and use /berserker
To activate the ability you need to either;
The ability gives you:
Once activated the ability will last for 30 seconds, although if you maintain your killing spree in line with what you need to activate it, you can keep it activated indefinitely.
Other stuff:
If you ever wish to remove the ability from a Battleaxe, use /berserker remove - you will not get any extra uses when you use this command.