Before children are introduced to books, they are taught individual sounds to construct words.
For example, when taught the sounds for the letters t, p, a and s, the children can build up the words "tap", "pat", "pats", "taps" and "sat".
Phonics is the word used to describe the sounds the letters make. In simple terms, the word 'cat' can be read from its three sounds: c-a-t.
These are not the names of the letters as we say them in the alphabet, but the sounds these letters make.
Likewise, the word 'thick' is made up of three sounds: th-i-ck, where pairs of letters combine to make a single sound. Similarly, 'rash' is made up of three sounds: r-a-sh.