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.
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.