Summarize this article:

Simultaneous solitaire is a type of double solitaire that allows for as many players as possible. Make sure that each deck is different and distinguishable from the others to avoid confusion. Remove the 2 jokers from each deck. It's important to make sure that every player properly shuffles their deck. If not, 1 player could have a massive advantage over the others. To shuffle, you can spread all the cards from a deck out on a table faced down. Mix them up with your hands and assemble them back into a pile when you're finished. Don't mix more than 1 deck at a time in a single area. If you're spreading the cards out, it's very easy for them to get mixed together. Simultaneous solitaire is played by everyone at once and revolves around speed. To ensure that the game is as fair as possible, use a whistle or a clap to announce the start of play. Players must place lower numbered black cards beneath higher numbered red cards and vice versa. With your stock pile facing down, flip the top card on the deck. Look at the card and look at the tableau and assess your options. You must place the cards in alternating colors in descending numerical order. You can only place cards in descending numerical order on top of each other. You cannot place a black 8 above a red 7. However, if you have a red 7 in your stock pile and a black 8 on the tableau, you can place the red 7 below the black 8.  For example, a jack of diamonds or hearts can only be placed below a queen of spades or clubs. You can send cards that you can't place from the stock pile to the discard pile. You can take cards from the piles in the tableau and place them beneath other piles. If pile 1 has a 10 of clubs and pile 5 has a jack of hearts, place the 10 of clubs below the jack of hearts in pile 5. Flip the last card in pile 1 upwards after you've moved the 10.  As the game goes on, you'll be using the tableau more and more. You will also need to move the cards on the tableau so you can access the face down cards in the piles. It's customary in solitaire to place all the aces in their own section of the playing area. To finish a pile, you need to place all of the 12 cards of each suit on top of their ace. For example, you have an ace of spades off to the side and you find the 2 of spades. Place the 2 on top of the ace. Do the same when you find the 3 of spades and so on. The winner is the first person to complete all 4 piles. If nobody is able to finish the game, the winner is the person with the most piles completed.  A completed pile consists of 13 cards from ace to king in the same suit. You can keep playing after the winner finishes to find out who comes second, third, fourth, and so on.

Summary:
Get a separate deck for each player. Shuffle each deck before play begins. Start the game with a whistle or clap. Make a move using the cards in your stock pile. Use the cards on the tableau to make a move. Place all aces off to 1 side when you find them. End the game when the first person has 4 completed foundation piles.