on = على
above = فوق
we can use the word على for thing on table, as example:
I'm sitting on chair = انا اجلس على الكرسي
we cant use the word فوق instead of على for the phrase context
for word فوق we use it to say that thing above another one they could be not in touch, for example :
the lamp above me = المصباح فوقي
i hope that is helpful.