Baby Children Balloon Hat Cap Slouchy Beanie Crochet Pattern

What does the abbreviation WDH mean? Also need to clarify where it says each round with single crochet begins with I chain each round with half double begins with 2 chains and each round with double begins with 3 chains but then a note say continuous rounds do not chain at the beginning so could you please help with this and anxious to get started on the hat. Thank-you