An example: Compare pit and spit. The first consonant of pit has an extra puff of air after it which is not found after the [p] of spit. This extra puff of air can be transcribed with the IPA diacritic for aspiration, a superscript "h":
In English, [p] and [ph] are allophones of the /p/ phoneme.
Switching allophones of the same phoneme won't change the meaning of the word: [sphIt] still means 'spit'.
Switching allophones of different phonemes will change the meaning of the word or result in a nonsense word: [skIt] and [stIt] do not mean 'spit'.
Different languages can have different groupings for their phonemes. [p] and [ph] belong to the same phoneme in English, but to different phonemes in Chinese. In Chinese, switching [p] and [ph] does change the meaning of the word.
A broad transcription uses only one symbol for all allophones of the same
phoneme. This is enough information to distinguish a word from other
words of the language. What details you have to include in a broad
transcription will depend on what language or dialect you are