As you use the top card on a stack it resurfaces the card which was underneath it. Rather than cards being dealt one at a time with 2 open piles, in this game the 24 cards in reserve are dealt 3 at a time across 3 stacks.
You can pair multiple cards from the tableau together, or pair one of them with the card atop the waste piles or on the free cell.
Like traditional Pyramid Solitaire you pair cards which add up to 13 to remove them from the tableau.