With a [Void] Void subclass equipped, defeat weakened targets, defeat targets with abilities, and cast your Super.
Some Void abilities weaken your targets. Weakened targets take increased damage, move more slowly, and fire less accurately.
To make progress, equip abilities, Aspects, Fragments, or gear with the Weaken keyword. For example, the Echo of Undermining Fragment adds a weaken effect to your Void grenades.
The utter emptiness of Void can be either horrifying or liberating. It is all a matter of perspective.