difference between simple  and compound preposition

Dear student,
The simple prepositions are the prepositions which are of one word only. 
The examples of the one word preposition or the simple prepositions are:-
against, at, among, beside, into, from, etc.
The prepositions which are of two-word or three-word combination are known as combined prepositions. 
The examples of the two-word prepositions or the compound prepositions are:-
According to, As of, aside from, because of, instead of, etc.
Three-word prepositions are:-
as far as, in addition to, in front of, on top of, etc.
Thanks
Regards