FreeCell is a simple but challenging game. The original version that shipped with Windows had 32,000 different patterns, and they've all been successfully completed except one! (You can try this game by going to the game menu, choose "Select Game" and enter #11982. Three of the four aces are buried at the bottom of a column of cards...)
It's helpful to know that most of the other games can be won - but it still takes some careful strategy. (In that regard it's similar to Spider Solitaire, another free game which also shipped with some versions of Windows.) But if you want to improve the odds that you'll win your next game of FreeCell, here's a couple strategy tips.
Find the aces which are closest to the top of a pile. Once you've freed an ace, it gives you one more place where you can move your cards. And this is more important than it seems. Every card moved from the lower board is one less card interfering with your movements for the remaining cards!
Identify important cards. Sometimes you'll see several cards that could all be moved up onto the suits pile if only you could reach the lowest card in that suit. At that point, it's worth counting up how many cards are blocking it in. Then notice how many of those cards can be moved away, and whether you could use the open spaces at the top of the board for any that can't. If you can free up that card easily, it's sometimes worth the extra effort. And if you move enough cards, you may clear out this column entirely, earning yourself another free space!
Try to develop all the suit piles at the same time. If the card you need has already been moved up into one of the suit piles, you can run into trouble. True, every card can be moved onto two other cards - the ones of the opposite suit that are one rank above it. But it's easy for one of those cards to be buried in a hard-to-reach pile. Sometimes even if I'm able to move a card from the bottom onto the suits pile, I'll wait a few turns until I'm sure I won't need it!
Build down. Imagine this. You've got four columns of cards, and each one goes all the way down from king to ace. At that point, you've already won the game, since you only need to move all the aces to the suit piles, and then follow them with the twos. But even if you don't get four 13-card columns, it will still make it easier to win. A long column of consecutive cards can be moved all at once, and it usually makes it easier to create an empty column, where any card can go.
Take risks. I'm convinced that some games can only be won after passing through a few tight moments where there's only one free space left. By planning ahead, you can usually pass through these situations, freeing up several valuable cards or creating more blank spaces. But if you're not willing to risk a few open spaces at the top of the board, you'll never make it!
It gets easier to win the more cards you move out, so take your time earlier in the game. And if you make a mistake, don't worry. Sometimes the easiest way to win is to simply go to the Game menu and restart your game!