Prepositions:

There are many prepositions for example: ABOUT (sobre, alrededor de, acerca de), ACROSS (a través de, al otro lado de), AFTER (detrás de, después de), AGAINST (contra), ALONG (a lo largo de), etc...

BUT, TO EXPLAIN THE CONCEPT WE´LL USE THREE EXAMPLES:

In / At  / On

In (places) :    I live in Santiago

In (time)    :    I always run in the morning

At (places):    He is at home

At (time)   :    He runs every morning at 6

On (places):   I´m on the bus

On (time)   :   I will see Ariel on his birthday