find() - Searches the string for a specified value and returns the position of  where it was found

Returns the index of the first occurrence of the specified substring.  Optional start and end indices can also be specified.

Example

Python
str = 'Python is a great programming language for great people.'
print(str.find('great'))
print(str.find('great', 20))
print(str.find('great', 20, 30))

Output

12
43
-1

Notes: Notice how the index returned is the absolute index of the source string, regardless of the specified start position.  Also notice that if the range does not include the substring, find returns -1.