It's a simple puzzle concept. Swipe different colored candies to match three of the same in a row. If you match four or five in a row you get a new candy that does more damage to the board. If you pair two of the new candies together, even more damage is done to the board.
There are more than 350 levels of Candy Crush and each has a different mission. Sometimes you're clearing all the "jelly" from a board, or white spaces. Sometimes you're helping specific icons (cherries or nuts) get to the bottom of a board. Other times you need to race to get a certain score in under one minute.
Whether you're just starting out or you're already addicted, there are some tricks everyone needs to know to progress in the game.