The aim of Freecell is to get 4 piles of cards - 1 in each suit - built from Ace to King. If you choose to play with 2 decks of cards then you will need to complete 8 piles.
The game starts with the whole deck dealt face up into eight tableau piles. There are 4 spaces for the foundation piles and 4 free cells for maneuvering room. If you choose to play with 2 decks of cards then you will have 8 spaces for the foundation piles and 8 free cells.
In Freecell, you may only ever move 1 card at a time. You can move any card onto any free cell or any empty tableau, and you may build the cards on the tableau down in rank and alternating colors. By customizing the game you can change how the tableau piles are built, and also what cards you can place on empty tableau piles. The lowest card in each column is available to play. Once the Aces are exposed, you can start to build the foundation piles, in ascending rank and matching suit. It is possible to move columns of cards if there are sufficient free cells or empty tableau piles.
Freecell is won when you have moved all the cards from the tableau to the foundations. If you run out of moves before winning, the game is over.