Reading and writing in alphabetic languages depend on sound-symbol correspondences, that is, relationships between letters and sounds. One of the chief ways of unlocking the mysteries of reading and writing for children is phonics, a method of instruction that teaches these correspondences and uses them to help learners in both these areas.
In English, there is not a one-to-one relationship between sounds and symbols. Each sound may be spelled by more than one symbol or symbol cluster, and a single symbol or symbol cluster may signal different sounds, depending on context. Phonics gives learners a statistically good shot at sounding out a word in a way that either matches what they know or is close enough that other clues, like context, will help them figure it out.
Phonics programs typically begin with sounds for individual letters and then teach them connected in words. Often, the material is artificial, with pages of, for example, three-letter words that all have a “short a” sound, and no context or narrative connection. Nevertheless, running together the sounds for the letters h, a — short in this context since it is followed by a consonant, and t, will likely produce something identical or very similar to an acceptable pronunciation for hat. Note that we cannot make too fine a point of many pronunciations, due to regional differences in dialect. A learner who recognizes that the word hat corresponds to the thing you put on your head and can pronounce it understandably while reading is doing just fine.
Whole language is the name of another pedagogical approach, in which the focus is on language in context. Students are more likely to be asked to recognize whole words in the context of real language situations, whether signage, household items, or story books. They also may be invited to put down their thoughts as best they can, using “creative” spelling, which is generally used as the focus of lessons in the correct spelling of the words the child chose, so that spelling lessons are personalized.
Some people understand phonics as a component of whole language, while other people understand them as diametrically opposed pedagogies. There are good reasons to combine the two, including explicit teaching of sound-symbol correspondences with opportunities to see and use language in context. And there are good reasons to allow learners to express themselves in writing before they are perfect and then show them the phonics rules that will help others to understand their communications.
Consider these two points. First, the fact is that adult native speakers who are experts in English do not read phonetically every word they see: words like stop on a stop sign are recognized by their configuration and context, just the points that whole language makes. Second, unless an adult is an exceptional human being or has very little occasion to express him- or herself in written language, he or she will likely misspell words now and again. This does not, and should not, keep the adult from written expression, and the same can be said of children. This argues for a combination of phonics and whole language approaches as the best language instruction.