During your turn you can play Treasure cards (cards with a -icon as their primary effect) from your hand to buy any face up cards from spaces 1 - 10 of the Market Board.
You can buy cards from the Market by paying the price indicated on the bottom right-hand corner, with any left-over still being usable until the end of your turn.
Treasure cards:
Once a face up card is bought (or otherwise removed) from the Market a new card immediately becomes available for buy; for spaces 6 - 10, draw a new card from the main deck to fill the empty space.