Well for starters I truly believe there's an afterlife. There has to be something more to life on earth, we have to be able to either be rewarded or punished for our actions on earth and that's where the afterlife comes into play. It's the decisions that we make today that will determine how our afterlife experience will be or better yet, where we go when we die.
What I don't know is how the afterlife is, or which afterlife people actually get sent to. I mean the Greeks had their own afterlife, with Elysium, the fields of asphodel and the isle of the blessed, the Egyptians had theirs, the Christians have heaven and hell and the Muslims have their own as well. It'll be interesting to see which one is the real afterlife.
I think the concept of an afterlife is closely related to religion and to believe in a particular religion is to believe in the existence of an afterlife. In fact if you've ever believed that ghosts exist then you most certainly believe that there's an afterlife.
I read a book by Rick Riordan a couple of years ago and in this book, the characters believed that whatever religion you believed in the most would be the determining factor of what afterlife you'd go to and maybe that's exactly what's going to happen. I'm a Christian so maybe when I die it's off to heaven(hopefully) with me. I guess none of us will know until we kick the bucket.
I hope this helps.