This is the standard-issue weapon from Jobe Research for your profession. You have to equip it to be able to use it. Right-click the weapon to equip it.
Click the Action button on the menu to open your Action menu. Select the Attack Actions sub-menu to find available combat actions.
To put an action (e.g. Start Attack) on your shortcut bar, left-click-and-hold the action, and drag it to the wanted location on the bar. Do this with the Brawl action - your weapon's special attack.
To initiate combat, target an opponent, for example a Leet or Reet of Paradise, and use the attack button in your shortcut bar. Take care not to be too far away from your opponent. Use the special attack button to perform your weapon's special attack.