Here is a very brief explanation. [ ] - represents a phone, an actual sound. / / - represents a phoneme, a meaningful unit of sound within the sound system of a language. < > - represents a grapheme, a unit of spelling. // // is a specialized subject. I won't address it. Examples (in American English): The graphemes < ph > and < f > have the sound [f] in English. The phoneme / p / has three allophones in English: [pʰ] (aspirated [p]) as in < pat >, [p] (unaspirated [p]) as in < spat >, and [p̚] (unreleased [p]) as in < tap >. With broad phonetic transcription, /p/ is represented by [p]. < pat > is pronounced [pæt], <spat> is pronounced [spæt], and < tap > is pronounced [tæp]. With narrow phonetic transcription, /p/ is represented by [pʰ], [p], and [p̚]. < pat > is pronounced [pʰæt̚], <spat> is pronounced [spæt̚], and < tap > is pronounced [tʰæp̚]. Also, here is a link to a useful IPA keyboard site. https://ipa.typeit.org/full/