You have inquired about how we leave our body and enter into the Spiritual Sky. This information is very nicely explained in the Second Canto of Srimad-Bhagavatam, First Chapter. The idea is that this universe is just like a coconut fruit, and exactly like the coconut fruit there is covering of several layers. Each layer is said to be ten times more than the other. So when a living entity is eligible and fully prepared to enter into the Spiritual Sky, he merges his different bodily elements which are called earth, fire, water, air, and ether. In those covering layers these bodily elements return, and the living entity goes back to the Spiritual Sky.
Letter to Vrndavanesvari, 26 April, 1969