[Mithalwen]

Hi Tom! From your question it seems you have read the Lord of the Rings but not the Silmarillion?

The Havens are not heaven but the Grey Havens (Mithlond) on the coast west of the Shire. From here Elves who are weary of life in the mortal lands of Middle Earth take ship and sail to the Undying Lands. So it is the departure point rather than the destination.

In Tolkien's universe there is an overall creator"god" Eru but the world is governed by angels or demigods called the Valar aided by less powerful beings of the same type called the Maiar. They have specific areas of responsibility like the Norse gods or the gods of Greece and Rome and live in the Undying lands, a sort of Paradise.

One of the Valar is called Namo or Mandos and he deals with judgement. When a elf dies his spirit is summoned to the halls of Mandos. If he refuses the call he will remain as a disembodied spirit - basically a ghost. If he accepts the call he will be judged by Mandos and spend and appointed time in his halls contemplating the deeds of his life and when appropriate will be given a new body and live again in the Undying lands. The Halls of Mandos are a kind of purgatory. Only one elf has returned to Middle Earth having died and gone to Mandos and that is Glorfindel.

It is more complicated than this because it is based on information and writings that weren't published by Tolkien in his lifetime and he revised his ideas about what happened to slain elves but I am sure someone will correct me if I have gone wrong.