1 deck. Easy. Unlimited redeals.
Stacks Solitaire uses 52 cards. The whole deck is dealt face down into 13 piles (stacks) with 4 cards in each pile. The top card on each tableau pile is turned face up and available to play.
Aces are moved to the foundations as they become available.
The top cards in tableau piles are available to play. You may build tableau piles down in suit. Only one card at a time can be moved. If you move all cards from a tableau pile it cannot be resumed.
When you have made all the moves initially available, click on the empty stock pile to restack cards. During restacking all the remaining cards are first gathered together and dealt out onto tableaus with 4 cards in each. Gathering and restacking doesn't change the order of the cards in the piles. If no moves are made, restacking reproduces the last deal. The process of restacking continues until either all cards are built up on foundations, or there are no more moves possible.