Phonetic symbols are used to represent, in print, the different sounds that make up words. While the international standard is that of the International Phonetic Association's International Phonetic Alphabet (IPA), publishing companies often make slight variations for their proprietary dictionaries and/or textbooks. There are also internationally agreed computer codings for phonetic symbols, other than those of the International Phonetic Alphabet.
The full chart of symbols can be seen (and downloaded from) here.
Likewise, the 'Extensions' to the International Phonetic Alphabet (ExtIPA) goes beyond the formal sound systems of languages, to cover the speech sounds of paralinguistic functions and pathological speech.
Many of the article pages below contain a section on "Anticipated pronunciation difficulties depending on L1". Some of these will also have links to pages that provide material for teachers to practise differences between "similar" sounds.
Phonemic symbols or phonetic symbols?
According to The Longman dictionary of language teaching and applied linguistics, 'phonemic notation uses only the distinctive sounds of a language (phonemes). It does not show the finer points of pronunciation. It is written with slanting brackets //.' On the other hand, 'phonetic notation is written in square brackets '.