1- How can a computer program know if this move or that move is better? It calculates all possbile continuation and examine? But if it does, how did it knows waht is the best continuation?

2- What is the estimate of the possible best continuatuons after every move? Is there a pattern, a sequence for it?

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Some more research effort would have been nice. – Epictetus Dec 13 '12 at 10:27
The Chess programming wiki may help you. For example the Alpha-Beta algorithm. Some level are examined only. Every position has a value (with ponderations for the different pieces). – Raymond Manzoni Dec 13 '12 at 10:28
en.wikipedia.org/wiki/Computer_chess has some discussion of your first question. – m_t_ Dec 13 '12 at 10:39

For question 1 The basics of computer player chess is it has value (coin weightage point) for each chess items and in the same way it has value(move weightage point) for each possible move for on chess item. With this it will decide which the best move is. For example if the opponent’s queen and pan are possible to cut-down in your next move the program suggest to cut-down the queen (coin weightage point for queen is higher than pan)