Prepositions indicate a relation between things mentioned in a sentence. Commong prepositions in English are on, above, below, before, after etc.. Prepositions come in a number of varieties but here we will discuss just place and time.
Place
[Some prepositions of place]{}
in
between
around
on
next to
under
left
right
in front
behind
Time
[Some prepositions of place]{}
after
before
now