This is a special attack that is only available to your profession. To use it properly, it needs to be easily accessible, and the best way to do that is to put it into your shortcut bar.
Left-click the "Jab of the Snake" icon to pick it up, and drop it into your shortcut bar.
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 and Dimach buttons - your unarmed special attacks.
To initiate combat, target an opponent , for example a Leet or a Reet of Paradise, and use the attack, brawl, and dimach buttons in your shortcut bar by right-clicking, or pressing the appropriate keys (1-10 depending on where in the shortcut bar you placed the icon). Take care not to be too far away from your opponent.