In Angry Birds, the player controls a flock of multi-colored birds that are attempting to retrieve their eggs, which have been stolen by a group of hungry green pigs. On each level, the pigs are sheltered by structures made of various materials such as wood, glass, and stone, and the objective of the game is to eliminate all the pigs on the level. Using a slingshot, players launch the birds with the intent of either hitting the pigs directly or damaging the structures, causing them to collapse and kill the pigs.
In various stages of the game, additional objects such as TNT crates, and rocks are found in the structures, and power-ups may be used in conjunction with the birds to kill hard-to-reach pigs.
There are several different types of birds used in the game. In the earliest levels, the red bird is the only one available. As the player advances through the game, additional types of birds become available. Some birds are effective against particular materials, and some have special abilities that may be activated by the player while the bird is airborne. For example, a yellow bird speeds up, a blue bird separates into three birds, a black bird explodes and a white bird can drop an egg-shaped projectile. The pigs themselves also appear in different sizes. While small pigs are relatively weak and are easily killed either by direct hits or by debris from the damaged structures, larger pigs are able to sustain more damage. In addition, some pigs wear hats or armor, making them even more resistant to damage.
Each level starts with the number, types, and order of birds pre-determined. If all of the pigs are killed by the time the last bird is used, the level is completed and the next level is unlocked.
If all of the pigs are not killed, the level is incomplete. Points are scored for each pig killed as well as for damage to, or destruction of, structures, and bonus points are awarded for any unused birds. Upon completing each level, players receive one, two, or three stars, depending on the score received. Players may re-attempt unlocked levels as many times as they wish in order to complete them successfully or to earn additional points or stars.
Source: Wikipedia
