A black six fits on a red seven. That is easy enough to remember. The more interesting question is which black six to move when both are available. Classic solitaire starts to make sense when you stop looking only for cards that fit and start noticing what each move leaves behind.
You can explore that difference in a browser game such as PlaySolitaire, or with a pack of cards on the kitchen table. The aim is the same: arrange the cards into four complete suits. Getting there involves more than tidying the layout, and a move that is allowed is not always the most useful one.
Know which part of the layout you are changing
In classic Klondike solitaire, the seven columns across the table are called the tableau. You build downwards there, alternating red and black cards. The four foundation piles work differently: each starts with an ace and builds upwards in the same suit. A cleared tableau column can take a king, including a correctly ordered sequence headed by one.
Those are different jobs, not competing versions of the same rule. Moving a card across the tableau can uncover something useful. Moving it to a foundation gets it closer to its final home. Before drawing another card from the stock, pause long enough to see whether the visible layout offers either opportunity.
Look underneath the card you want to move
Imagine that both black sixes are exposed and either can go onto the same red seven. One six is covering a hidden card. The other is the only card left in an otherwise empty column. Both moves are legal, but they do different things.
Moving the first six lets you turn over a new card. Moving the second creates a space, which may be useful if a king is ready to fill it. With no available king, that empty column cannot immediately accept anything else. Uncovering the hidden card is worth considering because it gives you information you did not have before.
This is not a rule that the hidden card always wins. It is a way to compare choices. Ask what becomes available after each move, rather than choosing whichever six happens to catch your eye first.
Have a purpose for an empty column
An empty column looks like progress. It gives you room to move a king and perhaps the sequence beneath it. But filling it with the first king you notice can close off another useful option.
If two kings are available, look at both ends of the proposed move. Which king is blocking cards you want to uncover? Which leaves somewhere useful for a queen you can already see? A red king can receive a black queen, while a black king can receive a red queen. That colour difference matters when only one queen is currently accessible.
You do not need to predict the entire deal. Try following the immediate consequence one move further. A space becomes valuable because of what it makes possible, not simply because it is empty.
Check before sending every card to a foundation
The foundations are the destination, so moving cards there feels satisfying. Still, a card can have a useful job left to do in the tableau. Suppose a black five is ready for its foundation, but an exposed red four needs somewhere to go. Keeping the five available may help you move that four and reveal the card underneath it.
Look for an alternative black five before deciding. If one is already available, you may have more flexibility. The point is not to hold everything back or to treat foundation moves as dangerous. It is to notice whether a card is still serving as a stepping stone for another move.
Talk through one choice, not the whole game
For families who already enjoy matching numbers in games such as Disney Pixar Rummy, solitaire offers a different question: what will this move uncover? If a child is interested in watching or playing, choose one visible decision to discuss instead of narrating every card.
Let the person playing move the cards and explain their idea. You can compare two possibilities without turning the session into a lesson or taking control of the mouse. Even a deal that ends with no useful moves can leave you with a clear discovery: the two moves that looked identical were doing quite different jobs.