That's pretty much what Rituals are...I use them to ask deities for help (I try to dothis only rarely), to thank them for help recieved, or on sabbats as part of the celebration.

The knives are used (For me anyways) to "cut" a "door" in a circle of energy once it has been raised. The circle is like a "bubble" of energy...half above ground, and half below ground. Walking through it would mess up the energy, so the knife is used to "cut a door" if I need to leave the circle for any reason. I also use it when releasing the circle, but I don't know how common that is. ^_^