Gaps is a popular solitaire card game, where the goal is to arrange the cards in order by suit from 2 - King. There are no Aces in Gaps because they are removed to create the spaces in the sequence that you use to arrange the cards.
Gaps is played with a standard 52 card deck. If you are playing with a real deck of cards (as opposed to our online version found above), you would first remove all the 2s from the deck and place them on the far left of your play area to begin each of the 4 rows. You would then shuffle the remaining 48 cards, and deal them into the last 12 positions in each row. When you have dealt all the cards, remove the Aces to create gaps in the sequence in the rows that the Aces happen to be in.
Once the cards have been dealt, you are ready to start moving cards into the gaps. Where there is a gap in the sequence, you may move a card into the gap if it is of the same suit, and one greater than the card immediately to it's left, or of the same suit as and one less than the card immediately to it's right. This gives you 2 possible moves for any gap, with the exception of a gap that is to the right of a King, or is in the last position on the right side of play.
As you play the game you will notice cards that form a sequence starting on the left with the 2s are highlighted. When you get stuck, you can have up to 3 reshuffles. This only reshuffles the cards that are not in sequence from left to right. In other words, all the highlighted cards stay where they are when you reshuffle.
In general it is not good to create gaps that are to the right of a King. This can limit your options as you go. Likewise it is not good to create gaps that are on the far right of play. This will also limit your options as you go. In some cases, this can be worth it, or unavoidable. Use your reshuffles wisely. In general you want to wait until there are no other possible moves before you click the reshuffle button.