it took a few reads to get what you have to do as somehow it doesn't stick in the brain.
but what Alban said was (of course) right
yep, just a phrasing thing too. Here's how I say/teach it:
Take the remaining parcel cards, they form the start of your auction deck. Then add auction cards to the parcel cards until it has 5 cards per player in it. That completes your auction deck.
(Do you have an auction deck that is mostly full of parcels? Don't worry, it isn't unusual for your auction deck to have more parcel cards than auction cards. Of course, this will vary by the parcels on the map and the number of players.)