Phonemes are the units of sound (speech) which distinguish one word from another in a particular language, they are discrete abstractions. In most varieties (accents and dialects) of spoken English there are about 24 consonantal phonemes and 20 vowel phonemes (altogether 44 phonemes), but only 26 letters in writing. To learn all the phonemes in English, it would be better to use the IPA, which has a unique letter for every phoneme in English, unlike the English alphabet. The development of phonological representations for words and their parts is a major step in learning a spoken language.
A good way to learn phonemes in a language is to learn minimal pairs. A minimal pair is a pair of different words that are different by only one sound. An example of this is "bit" and "bat". Even though only the vowel in each word is different, each word has a completely different meaning. Another example is "dip" and "tip", where both words have different meanings even though only the first consonant in each word is different.
- Concise Oxford English dictionary, p1027.