In chess, check is an attack on an enemy king; this attack can’t be ignored. If the check can’t be neutralised, it is checkmate and the game is over. Stalemate occurs when one player has no legal moves, but his king isn’t in check.
Here are a few additional details on check, checkmate, and stalemate in chess:
The first lesson you must learn on the road to improving your chess game is to get your priorities straight.
Not only should you not be trying to checkmate your opponent in the opening, but you shouldn't even be trying to win material (that is, to gain advantage in the relative value of your pieces). Save both objectives for later in the game. The primary objective of the opening is the rapid deployment of your pieces to their optimal posts. You can't put a piece on a good square, however, if that piece can easily be driven away by your opponent's pieces. So getting your pieces not only on good squares, but also on safe squares, is critical to your opening game.
The rapid mobilisation of pieces is called development. Development is not considered complete until the knights, bishops, queens, and rooks are moved off their original squares. Normally, getting the knights, bishops, and queen off the back rank also is important. Rooks may be effective fighting from their starting rank, but the other pieces usually increase in power only as they move toward the centre.
Control of the centre and centralisation of your pieces are critical objectives in a chess game. The pieces generally increase in power as they are centralised. In the opening phase, you want to try to maximise the power of the pieces in a minimum amount of time. Moving one piece three times to position it on the best square doesn't help much if, in the meantime, your other pieces languish back on their original squares.
Just as important as developing quickly is preventing your opponent's development. Some otherwise strange-looking moves can be explained only in this way. If you waste two moves to force your opponent to waste three, well, those moves weren't wasted after all! This idea brings up an important chess maxim: Don't get so caught up in your plans that you forget about your opponent's moves. Just as you are, your opponent is trying to interfere with your development while developing his or her own pieces — at your expense.
As you become familiar with the game, you begin to pick up on a few basic principles of opening play, not only from your own experiences, but also from other players. (Remember, however, that many such principles are just guidelines — don't think you're bound by them. If, for example, your opponent slips up and gives you the opportunity to deliver checkmate, do so! Don't worry that such a move develops your queen too early!)
Pachman goes on to caution against applying these principles dogmatically. He teaches that the real meaning of development is not how many pieces you bring out but whether you develop your pieces to maximise their power.
Source: Chess for Dummies