Turn 3, also called Draw Three, is Klondike with the stock turned three cards at a time. The game above is set to it. The tableau and foundation rules do not change, and the rules page lists them. What changes is which stock cards you can reach, and that makes the stock a puzzle of its own.
A click on the stock moves three cards onto the waste. Only the top one of the three can be played. If you play it, the card under it becomes playable, and so on. If you play nothing, the next click covers all three with three new cards. At the start the stock has 24 cards, so a pass with no plays shows you exactly 8 playable cards: the 3rd, 6th, 9th and so on. The other 16 stay out of reach on that pass. When the stock is empty, the waste turns back over and the next pass starts. This site allows unlimited passes.
Each card you play from the waste shifts every later group of three by one position. A card that was in the middle of a group on this pass can be on top on the next one. This is the main skill in Turn 3: choosing plays from the waste so that the card you need comes up on top.
Fewer Turn 3 deals can be won than Turn 1 deals, even with perfect play. Some deals are lost because the one card you need sits in a group you cannot reach, and nothing in the tableau gives you a play that would shift the groups. Expect to win noticeably fewer games than in Turn 1.
The tableau advice in the strategy guide applies in both modes.
Turn 3 suits players who already win most Turn 1 games and want each deal to take more thought. It also suits anyone who wants the game the way it starts on this site, since the draw buttons default to Turn 3. If you are still learning which moves matter, start with how to play Solitaire and Turn 1.
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