Always define your terms: that is what I learned when I was learning how to be an English teacher. This remains a very useful thing to remember both as an educator and as a writer; I was actually given special workshop training in writing the type of essay that Arizona students have to write in order to pass their AIMS tests in their junior year. That opportunity came to me when I was teaching sophomores at Cholla Magnet High School in Tucson, preparing them for the AIMS test the next year.
You can think, on first blush, that Christians have their definitions and that they are easily understood. Especially for those who think that they take the Bible literally, the terms like "resurrection" and "ascension" are often assumed to have much more specific meaning than they actually have.
Throughout history there are some few individuals who have left this earth in their physical bodies. The ones that I know of are Elijah, who sent to heaven in a "chariot of fire;" a mysterious figure called Enoch; Moses (perhaps), and Jesus. Jesus differs from the other three in that he left this earth in a resurrected body.
Generally speaking, Moses is believed to have died and been buried in a spot that was lost to history, just before the Hebrew people crossed into Israel. So we can't technically include him in those who actually went anywhere because we believe that he did die.
The term for this leaving of Planet Earth in a physical body is referred to as Ascension. Specifically, Christians believe that Jesus rose bodily from the surface of the earth towards the heavens until a cloud (schechinah) cut him off from the sight of his followers. The word isn't necessarily as simple as the concept of a cloud, though, and there is discussion as to what it means really happened.
Some Christians are unable to believe in the Ascension at all. The more cynical among them suggest that when the Church was foolish enough to bring Jesus back to life in the Resurrection story, they acquired the problem of what to do with him, since by the time the Gospels were written he was obviously no longer around. So we don't really know what happened to Jesus after he was crucified. There are different stories and even more possibilities.
The simplest possibility was that the Romans tossed him into a lime pit and covered him over with dirt and the next day's execution victims. Another possibility is that someone bribed the Roman government to release his body to someone, either to his family or to a person who made the humanitarian gesture of returning him to his family. That outcome provides an explanation for the tomb stories.
But neither of these possibilities explains the extraordinary nature of Jesus' appearances after his death. He could appear out of nowhere, it is written. He could pass physically through a locked door. His wounds were still present on his body. He could eat. These stories are so implausible and odd that many modern scholars simply discount them.
However, my attitude has always been that we shouldn't dismiss out of hand stories that pass down through many generations. The amateur archaeologist who discovered Troy did so by following the account of its location in Homer's Iliad. And then there is the fact of the existence of the Shroud of Turin.
So what I would say to anyone who is giving Christianity a fair consideration is to keep an open mind. Those who would cleanse Christianity of all its mysteries are very likely to be throwing out the baby with the bath water; we don't know enough to say what did and did not, nor what could and could not happen. If the early Christian stories prompt you to begin your own course of reading and study, so much the better. I got where I am now, which is by no means exceptionally advanced, by reading and learning about what I want to know about the Church: its history and theology.
But the best place to start is with basic Christianity. The primer of the Faith is generally agreed to be Mere Christianity by C. S. Lewis, and it is available for very low prices at Internet bookstores, even if you want a hard-cover copy. I don't know how many copies I have bought over the years and given away; I wish I had a copy now to re-read and refresh myself at the crystal-clear source of Lewis' theological thought.
But if you follow the ancient-astronauts believers, the UFO studies, the pre-history of the human race or any of the mystery pursuits, you will come to believe that there is just more to this life than we know, and possibly more than we can know due to the nature of human thought and comprehension. We do not know today why about 10% of the human race at any time is gay. We don't really know whether Atlantis existed or not, and there are now a few possible locations for it, not to mention the actual underwater ruins that have now been discovered off the coast of Asia. So we ought to study rather than pronounce that all doors are about to be closed; that's my belief.
Today I saw an interview, that I was unable to read because it was a pay-per-view video rather than a transcript, in which the author referred to "the prison of belief." I think that is a well-turned phrase, as long as you remember that religion is by no means the only such prison; unbelief can be every bit as dogmatic and anti-intellectual as faith.