This is what the Oxford dictionary (http://www.oxforddictionaries.com) says about its usage: “The preposition “upon” has the same core meaning as the preposition “on”. However, in modern English “upon” tends to be restricted to more formal contexts or to established phrases and idioms, as in “once upon a time” and “row upon row of seats”.”

We don't use upon much. Use "on" or "up on". The cat jumped up on the table. "Upon" is somewhat poetic: Once upon a time, there lived a fair princess. (fairy tales) Well, upon my soul! (exclamation)