Why do I need a knife... Who are we sacrificing?

On your altar there is optionally what is called an athame or small black handled knife. That can be used in a couple different ways. So far I have seen it used like this:

• dipped in saltwater and used to draw pentagram at the four corners of a circle
• and to make the initial saltwater mixture... like a spoon

Important misconception to get out of the way, wiccans do not sacrifice living things, animal nor human not even dead. We give back usually by food offerings, wiccans aren't violent and are more fine-tuned with nature so why harm what's in it to honor it? It's be dumb. So no sacrificing sheep, that's not what the craft is for.