A player deck is very similar to a computer deck.
A players deck will only be used in quest mode! The difference between a players deck and a computer deck (or a quick player deck) is, that it is based on a limited heap.
When building a computer deck all possible cards are accessible as many times as you like.
A player has only as many cards in the heap as he was able to collect untill now.
All things said in relation to the computer deck are the same with exception of:
The deck is build for the active player (if no player is active - you can not build a player deck)
the deck is only availble for that player
the heap (on the left side of the screen) is reduced by the cards you put in the deck (vice versa)