4 candles (same color)
You need 4 candles, all the same color. Make sure they will be able to burn during the entire ritual or whatever you're doing. The color should be something you identify with as power. Even though I'm performing a Dark ritual I usually use white candles. White represents light, and without light there could be no true darkness. The instant of creation was bright white and as we've seen in things like the explosion of the Atomic Bomb destruction can be a bright white as well.
Set the squares at the four corners of your majik space, your room, or something you want to confine in the protected space.
Ignite them going counter clockwise, calling out to a dark spirit for each candle.
If you have a particular entity like a guardian demon to call upon, do so while standing in the middle.
At the end of your rite, extinguish the candles in reverse order, thanking the entities for their help.
As a precaution, do not try this with very unique and distinguished demons. Do not, for example, summon Choronzon into one of the corners because it will never balance out with the other three. If you want to call down someone as powerful as Lucifer be sure to do the same in all the corners. The higher ranking the demon the stronger you have to be and it helps to have both a good reputation and a good reason to summon them. Unless you overpower them and force them to stay there and guard you they're there because you asked and they chose to come help you.