Phonics instruction teaches the relationships between the letters of written language and the sounds of spoken language. Children's reading development is dependent on their understanding of the alphabetic principle — the idea that letters and letter patterns represent the sounds of spoken language. "Decoding" is the act of sounding out words using phonics.

The goal of phonics instruction is to help children learn the alphabetic principle — the idea that letters represent the sounds of spoken language — and that there is an organized, logical, and predictable relationship between written letters and spoken sounds.

Learning that there are predictable relationships between sounds and letters allows children to apply these relationships to both familiar and unfamiliar words, and to begin to read with fluency.

Children are taught, for example, that the letter n represents the sound /n/, and that it is the first letter in words such as nose, nice and new. When children understand sound–letter correspondence, they are able to sound out and read (decode) new words.