Gaps is an awesome, but not very well known solitaire card game. It's a super easy game to learn how to play and I'll put out a video tutorial soon if you've never played it. For right now I'll right up a quick summary of how to play.
Gaps Solitaire starts with the cards dealt into 4 rows of 13 with the 2s moved to the far left of the game and the Aces removed to create 'Gaps'. Your goal is to try and put all the cards in order from 2 to King by suit. The way you do this is by moving cards in to 'Gaps'. You can move a card into one of the 'Gaps' if the card is one more than the card to it's left and has the same suit, or is one less than the card to it's right and has the same suit. You can also move a card into one of the gaps if it is one less than the card to it's right and has the same suit. As you get cards in order, those cards become highlighted. You can shuffle all the cards that are not highlighted up to 3 times in a game by clicking the 'Shuffle' button. You will almost certainly have to do this at least once in a game because you get stuck. The easiest way to get stuck is to get most of your gaps directly to the right of a King, since there is no card that has a greater value than a King.