Uh, ok. Well, immanence isn't terribly simple, but this is the best summary I can think of. The immanence of God is the belief that God is in Everything and Everything is God. You and I, are both part of the greater whole of the Almighty and in truth all have the spark of divinity within us. We are, literally, part of God. The truth is, that almost every major religion today (Excepting Buddhism somewhat) believe in the immanence of God, to a greater or lesser extent; for instance, it is a very very big deal in Hinduism, and also in more mystical gnosticism-like religions.
It is perhaps summarized by this statement:
"The Spirit of the Creator is inherent in me, but I am not he"