"Find" Formula Field Confusion

"Find" Formula Field Confusion

Hello,
 
I am having trouble finding out what the "1" means in the "Find" formula field.
 
Returns the nth occurrence of the text string. Find('string','search string',number) Find('greenery','n',1) returns 5
 
I understand why it returns "5", because "n" is the fifth letter in "greenery", but what is the "1" for?
 

Alex O