It's so hard to be definite on this one. There are infinite possibilities, really. But my version of it goes something like this:

We are spiritual beings, and incarnating as human is just one part of our experience. We really are so much more than just this one lifetime. We existed before and we will exist after. We exist above and below and all around this one incarnation. And when it is over, our souls will continue on. We are our souls- that is who we really are. Life here is something of a dream, in a way.
I believe in reincarnation- from my perspective, I know without a doubt that it happens. What we call "heaven" is a human interpretation of the blissful aspect of the divine. The "gates of heaven" refer to the the doorway into the divine that we experience through death, or through profound meditation or spiritual awakening. When I use the word "God" I am referring to what I call "the light". It's the source, it's the sum total of it all, it's loving and bright and beautiful and dynamic. I have seen this light; I know it is there. There are beings that operate within it, to it and from it, as messengers and guides. These beings are the angels. They are not human, and they can be very helpful. They are radiant. I have seen one of them and it was like nothing else I have ever seen.
When we die, we go through a process of spiritual transcendence of the body. We shed the body and return to our more pure form, which is the soul. In doing this, we go through a series of stages. In one or more of these stages, we process the life left behind. This is the process we call "purgatory". It is called this name because here the soul is essentially purged of its earthly life. We process and release all of our deeds, and we experience the truth about ourselves. It can be very painful, but we need to do this in order to release from the body and the lifetime. Failure to transcend through this stage can result in an earthbound state, which creates ghosts.
We can and often do go through stages of this "life review" process while we are alive. In truth, death is simply a magnification of what occurs in life. If we work on ourselves and face our truth, though it may be scary, we will do the same in death and we will pass through the stages and go straight into the light of the divine. If we run away from ourselves and fail to face our truth, it will be particularly difficult for us to in death to purge and move on.
My experience has taught me that there is a realm in which beings who shun the light of the divine tend to cluster. This realm is shut away from the light because the beings who cluster there have no wish to be near the light. There are some powerfully negative beings there, and there is a conscious effort of some sort to maintain a boundary which wards off the light. The beings in this place are often in a state of great pain and suffering. I have seen some of them, and I call them demons. There are dark entities there which do try to reach out and encourage vulnerable souls to join them. One way they do this is by taking advantage of compromised individuals and coercing them to do things that are destructive to the soul, such as suicide. Many extremely suicidal people report hearing voices telling them to kill themselves. These voices belong to the dark entities from this realm.
God is all loving, and there is always a sense of unconditional compassion and forgiveness emanating from the light for everyone- including the dark entities. The divine light is made of love, and beings who enter into this light are at once immersed in a sea of love, the most profound and glorious love we as humans could ever possibly imagine. Its vastness is almost imperceptible to us. To comprehend it our minds have to strain, and they sometimes break in the effort.
There are so many questions to be answered which touch on the realm of the soul. There are answers, but they strain the boundaries of our human consciousness. Some things we are not meant to comprehend in this life.