C++ :: Erase Part Of The String?

Code:
// string::erase
#include <iostream>
#include <string>
int main () {
std::string str ("This is an example sentence.");
std::cout << str << '
';
str.erase (10,8);
std::cout << str << '
';

Code:

Output:

I don't understand this program. What do these 2 numbers represent? The index of an element in a character array? The 10th character of the array is 'n' and 8th is a "space".