The word 'upon' has the same meaning as 'on'. If you see 'upon', just read it as 'on' and you won't have any problems. You will never actually need to use this word. 'Lorn' is not a normal English word. Are you sure that this is the word you have seen?

Lorn? Check out the spelling of that word. It could be a name but it's not an English word that we use these days. Upon. Yes, this is a word. I sat upon the chair = I sat ON the chair. You'll meet the word in novels and poetry, and in some expressions. "Once upon a time there was a princess and a frog...... " Really you can simply take the 'upon a time' out of the sentence. Once there was a princess and a frog..... " As SuKi says, you won't need to use this word much at all, but you will meet it sometimes.