To do this, you must wait for your initial nebula to generate sufficient units (colored dots). Once you have a few, you should send them to conquer new nebulae, which might be 'free' or conqured by an enemy color.
To snatch a nebula you just have to send enough units to destroy the enemies and the resistance of the nebula itself.
Auralux is a beautiful game, with very simple but beautiful graphocs; a very relaxing soundtrack, and extremely simple and fun gameplay.
You can only play the first level.