Suppose you are given a string and you want to count how many times each letter appears. There are several ways you could do it:
You could create 26 variables, one for each letter of the alphabet. Then you could traverse the string and, for each character, increment the corresponding counter, probably using a chained conditional.
You could create a list with 26 elements. Then you could convert each character to a number (using the built-in function ord), use the number as an index into the list, and increment the appropriate counter.
for the 2nd part I don't understand what using the ord function has to do with indexing to the list. since ord return the unicode of the character not an index.