Empty a column
An empty column is the strongest thing you can own in FreeCell. It takes any card, so it is a free cell that also lets you unload a run onto it — and, unlike a free cell, it doubles the number of cards you can move in one go.
Why it doubles
The limit on a run is (1 + empty free cells) × 2^(empty columns). Each empty column multiplies, each free cell only adds. Four open cells and no empty column lets you move five cards; four open cells and one empty column lets you move ten.
What it costs
Emptying a column usually means breaking up a tidy sequence you built earlier, and beginners hate doing it. Do it anyway. A neat run of six cards that you cannot move is worth less than a hole you can put anything into.
Keeping it
Once you have one, do not fill it with the first king that comes along. Fill it when the card going in is one you need to move again soon, or when filling it unblocks something underneath.
A common mistake
Filling a fresh empty column with a single card just to tidy up. Unless that card unblocks something straight away, you have handed back the doubling for nothing. Kings are the classic case: a king at the bottom of a column never needs to move again, so put one there only once you have decided the column belongs to it.
On a real board: deal 4
This is deal 4 after 14 hints, exactly as the board draws it. The solid outline marks the card the next hint moves; a dashed outline marks the card it is working towards.
On the board, this one reads: That empties the column. You can move 2 cards at once now, instead of 1.
The hint moves the 3♦ onto another column, and the column it came from is left empty. The free cells do not change, yet the number of cards you can move at once goes from 1 to 2. That is the formula at work: one more empty column, and the limit is multiplied by two.
Play deal 4. Open it and press Hint 14 times to reach this spot.