I can't remember when I started reading Katherine Mansfield. I have been reading her all my life – her short stories were read aloud to me by my mother, and then I read her through my school years and beyond – so it's hard to know when the fact of her meticulously made short fictions was first made apparent to me.

But I do remember coming across Prelude, her only novel – novella, really, a long, long short story made up of scenes a bit like chapters – published by Virginia Woolf's Hogarth Press in 1918. This edition I found, when I was about 12 or 13, among the books on the shelf, a dull-looking cloth board volume that I think must have been my mother's. I opened it up, turned pages that were thin and yellow as an old bible, and sat down in a square of sunshine on the living-room floor and began to read.

"There was not an inch of room for Lottie and Kezia in the buggy…"

Prelude is the story of a family who are leaving their house in town for life in the country, all told through the eyes of one of the younger daughters, Kezia, who observes every single little thing as one home is dismantled and another set up to take its place. Mansfield builds up a domestic world as rich and varied and idiosyncratic as life itself, a story made entirely from the seemingly inconsequential moments, overheard conversations, half-realised thoughts… with no almighty sense of plot or drama, only the long hours ticking past in a long day.

What I understood then, in that first reading of a book I have returned to over and over, is that it's not only short stories that may have the power of second-by-second reading – where every detail, every line, is of concentrated importance. I was reading what it was to be in the world – observant and sensitive to its textures, sights and sounds. Until then I had thought that all novels had to have a plot, a cast of characters that marched in time to authorial will, each chapter like the compartment of a fully-loaded goods train. Here instead was a narrative made up of tiny details that could go anywhere, mean anything – "moments of being" Woolf, Mansfield's fellow modernist writer, called them.

Now I know this is the mark of all great fiction. To have a world be given us that is not just a place we look at, or learn about, or derive entertainment from, but feels as familiar as our own. So I learned, sitting in a square of sunshine from my childhood, reading, that for me the most interesting kind of story was, like life, not something ever known and understood and fixed by its shape of beginning, middle and ending, but an opening, a door that lets us in. Prelude was the start.

Kirsty Gunn's novel 'The Big Music' is published by Faber & Faber