there is a part of the sentence that I don't understand in my book: "When the bell rang, a nasal buzzing sound, a gangly boy with skin problems and hair black as an oil slick leaned across the aisle to talk to me".I wonder whether it means that bell doesn't work well or actually the sound came from the boy. Thanks
'a nasal buzzing sound' describes the sound of the bell. Most bells go 'ding' or 'dong', so depending on when they are (maybe a school), this 'bell' may actually be a 'buzzer'. A 'buzz' is usually 'zzzzz', but this 'buzzing sound' is more 'mmmmm' or 'nnnnn'. This is reasonable sound for a buzzer to make, but an unusual sound for a bell to make. But it doesn't, by itself mean that the bell doesn't work well.
It is possible for a noun phrase there in the sentence to describe the boy (for example 'When the bell rang, my best friend, a gangly boy ...'), but keep 'bell' and 'sound' together first.