Although no one can "know" what happens after death, the way life works could lead us to draw acceptable conclusions.
I think everyone would agree as to what happens to your physical body, because it's entirely observable - the body rots and is returned to the earth, in a fashion, over a period of time. The nutrients of which is to be used again by vegetation surrounding the area, drawn from the ground and via the creatures that feed on the body. That bit is simple science.
It's the "spirit" of a person that people wonder what happens with, and without any scientific evidence, it's not hard to see why people would have many varying hypothesis as to what happens to a person's "spirit". Here is where the acceptable conclusions I spoke of come in. While we're alive, our conciousness is infact just electrical signals caused by chemical reactions interpreted by the synapses in our brains. When the brain dies, these chemical reactions and electrical signals obviously cease, thus ending our conciousness (or what spiritual people would refer to as our Spirit). While, like I say, no one can know what happens when we die, simple scientific knowledge concludes that we do, indeed, simply end/cease to be.
I can understand fully why people might have issue with that, as the human mind is a feeble thing and is genuinely incapable of understanding "nothingness". When thinking about it, mosrt people probably think of pure blackness, or something similar. With our inability to comprehend "nothingness", it's very easy to see how that would lead to the idea of people having a spirit that carries on eternally.
My own personal way to look at it is; I don't remember being bothered by the fact that I wasn't alive, before I was born, so I can't imagine I shall care once I have died, either.
I know I'm rambling, but I like to talk, so you'll have to deal with it