Words are made up from small units of sound called phonemes. Phonics teaches children to be able to listen carefully and identify the phonemes that make up each word. This helps children to learn to read words and to spell words
Children are taught to be able to blend. This is when children say the sounds that make up a word and are able to merge the sounds together until they can hear what the word is. This skill is vital in learning to read.
Children are also taught to segment. This is the opposite of blending. Children are able to say a word and then break it up into the phonemes that make it up. This skill is vital in being able to spell words.
What makes phonics tricky?
In some languages, learning phonics is easy because each phoneme has just one grapheme to represent it. The English language is a bit more complicated than this. This is largely because England has been invaded so many times throughout its history. Each set of invaders brought new words and new sounds with them. As a result, English only has around 44 phonemes but there are around 120 graphemes or ways of writing down those 44 phonemes! Obviously we only have 26 letters in the alphabet, so some graphemes are made up from more than one letter.
Another slightly sticky problem is that some graphemes can represent more than one phoneme. For example 'ch' makes very different sounds in these three words: chip, school, chef.