Please explain the meaning of this quote about seeing creation in a single grain of sand in The Alchemist by Coelho."you dont have to understand...

What this quote is saying is that everything in the world
is connected and that you can learn everything you need to know wherever you are. 
Because of this, a person should look at their own surroundings to learn about the world
-- they do not need to seek the truth anywhere else.

In
this passage, Santiago is talking to the alchemist, wondering how he can best achieve
understanding.  The alchemist is telling him that understanding can be achieved right
where he is.  The alchemist is saying that everything in the world can be understood by
looking at any little part of the world.  This is true because everything in the world
is connected and so each bit of the world is a microcosm of the
whole.