There are eight foundations, but you cannot play to them. All building happens on the tableau only. When you arrive at a full-suite sequence of thirteen cards, discard it by moving to a foundation. To win the game, you must discard all eight sequences.
Tableau has ten columns. Reorder cards in tableau so as to build them down the ranks. Play Queen of Spades on a King of Spades, for instance. At any given moment, you can move the last card from any column to another column, if ranking permits. You can also move whole or partial sequences of cards ordered by descending ranks. No cards can be placed over Aces, and Kings only move to empty space. Spaces accept any cards and ordered sequences of cards.
When you click on the stock, a whole new row of cards is dealt to the tableau. Spider does not allow redeals.