Void meditation helps you to gain control of your thoughts which is important for a Satanist because as we develop spiritually our thoughts get stronger and manifest in reality easier as opposed to someone who doesn’t practice power meditations.
and it’s good for getting the mind under control which helps one be able to focus better when doing magick.
but you should also be doing power meditations in general to empower your soul. IE open your chakras, clean your aura, build protection etc.
The meditations on the JoyofSatan website are self explanatory, all you need to do is follow the steps like how they say to do. and if there’s something that you don’t understand you can come back here and ask.
ideally you want to start with the beginner section of meditations, obviously.