how does rabin karp algorithm work code example

Example: rabin-karp algorithm

1 function RabinKarp(string s[1..n], string pattern[1..m])
2     hpattern := hash(pattern[1..m]);
3     for i from 1 to n-m+1
4         hs := hash(s[i..i+m-1])
5         if hs = hpattern
6             if s[i..i+m-1] = pattern[1..m]
7                 return i
8     return not found