Phonetics and the IPA, Chapter 1, Exercise 3
Sample answer.

(a) the word as spelt in a book: italics, e.g. pin (ordinary spelling needs no brackets)
(b) the puffed-out p of "pin": square brackets, [pʰ], because it is a physical sound
(c) the phoneme English speakers hear as the first sound of "pin": slashes, /p/, because it is a unit of the language's system
(d) a dictionary entry: usually a broad transcription, in square brackets or slashes depending on the dictionary's convention; many British dictionaries use the IPA for it.