[Elspode]

There's no all-encompassing answer for this question, but I'll describe things from my own point of view:

1) First off, I don't cast spells *on* people. I protect myself. I protect my family. I ask for the Universe to see that people learn the lessons they need to learn. The practices of non-Wiccan witches almost certainly differ from my own.

2) A spell can be a prayer, yes. It can be that simple. However, the classical view of a prayer is that you offer it up to some other entity/deity and ask them to "make it so, #1". In my universe, I am effecting change through the power of the energy of my consciousness and my intent. If you can find it, watch the film "What the $@*!& Do We Know? (usually referred to as "What the Bleep Do We Know"). While not the perfect vehicle for the notion of magic as manifestation of quantum mechanics, it is at least a good thought-provoking presentation. I also usually recommend "The Holographic Universe" when discussing this topic.

3) What goes around does indeed come around. This is precisely why I do not cast spells on people unless there is no other choice, and they are a threat to me or my family...and even then, there's almost always a way to make it indirect. Nevertheless, there's a price to pay somewhere along the line for what one does, and one needs to be prepared to pay the piper when he plays one's tune.

I'm guessing that there is a reason you are asking this?