What is the difference between On and Upon ?Feel free to just provide example sentences.

They mean basically the same thing, but there are a lot of circumstances where only "on" is appropriate, so it's better to stick with "on" if you're not sure which one to use. "Upon" often sounds old-fashioned, and there are many idiomatic phrases where only "on" can be used. "Upon" is also usually about being literally on top of something, whereas "on" is used more broadly.

For example, you can be "on the phone" but you can't be "upon the phone" unless you're sitting on top of the phone. If you were riding a train, you could say, "I was on the train," but "I was upon the train" would mean that you were literally on top of the train, on the roof of the train.