Simply visit each interview and leave a valid comment for the author and you are then eligible to enter that author's giveaway.
Each Featured Author Interview has it's own contest so you can enter as many or as few as you like. One contest is open to worldwide entrants; one for USA, Australia & NZ; the others are for residents of the USA only. Feel free to spread the word!
Contests run from August 26 - September 12 NZDT.