Thanks for your note to us here at TruthBook about these terms. I will do my best to define them for you.
URANTIA: "Your world, Urantia, is one of many similar inhabited planets which comprise the local universe of Nebadon."
Read more about Urantia in the Urantia Book.
MORONTIA: Morontia is a term designating a vast level intervening between the material and the spiritual. It is not material or spiritual, but somewhere in the middle of those two.
Click to read more about morontia life
NEBADON: Our local universe (Nebadon) is made up of one hundred constellations, ten thousand local systems, and about ten million inhabitable worlds.
Read more about local universes
SALVINGTON: "Salvington, the headquarters of Nebadon, is situated at the exact energy-mass center of the local universe [Nebadon]. But your local universe is not a single astronomic system, though a large system does exist at its physical center."
Click to read more about Salvington
These are pretty simple descriptions, but you can much, much more about all of these terms by clicking on the links I've given you and also by making use of our search feature HERE.
You can use this search feature from any page on our site, too; just look in the upper right corner. The top line is for searching our whole site for specific subjects/pages (like angels, life after death, Adam and Eve, etc, etc) and the bottom line is for searching only the text of The Urantia Book for words and/or phrases.
Finally, HERE is a good 5-minute video that might also be helpful to you in understanding some of these terms and the vast distances that are involved in the universe as revealed in The Urantia Book.
Thanks again for your question; I hope my reply has been helpful to you. Please feel free to write back again if you have any other questions.