on 與 upon 的分別

Main Difference:~
When something is ON something, it means currently at the same level or just above.
e.g:
I live ON the fifth floor.
The book is ON the table.

Upon simply means above. It is less physical. It is normally used on things that you cannot touch.
e.g:
The language of this book is UPON my understanding.
The theory is based UPON this book.