Add the punctuations:
Three of the islands-Hawaii, Maui, Oahu-contain most of the major cities David.

Should I have comma after “Oahu” and “contain”?

If you could, please tell me why they put David at the end. It doesn’t make sense to me.

Yes you should but a comma after Oahu but not after contain. The reason why David is right there is unknown but I'm thinking it was a spelling error.

Explanation:

although there are different versions for the fairy tale little red riding hood,   as the one from grimm brothers and perrault, all of the versions show the huntsman as a man who is in perfect harmony with nature. the statement that best describe him, the huntsman, is that he is a true hero who inspires those around him due to his words and actions. the way he acts show internal reflections that are an example to follow by anybody who takes the time to analysing them. he shows altruism actions when he aside puts his job just to check the grandmother is well, by doing this he could notice at an early stage what has happened and could save her.