“Small moments” is a phrase I am borrowing from elementary school teachers. To teach kids how to write a story with a beginning, middle, and end, the teachers tell the kids to pick a small moment from their lives, like losing a tooth, riding a two-wheeler for the first time, a special gift, etc. Choosing a small moment to write about is good advice for any beginning writer of any age. To qualify as a small moment, the event should have taken no more than a half hour of time and should have happened to you personally.
When you write down your small moment for the first time, you can either write just a summary with a beginning, middle, and end, or you can write the whole event as thoroughly as you can. Follow whichever approach feels more natural to you. If you take the first, your summary is your outline to which you will add details. You may want to write several versions, each a little more detailed than the last.
Personally, I like dumping everything on a page and then going back and editing. My background as a librarian might have something to do with my preference. I always liked to weed out of a library’s collection any old, damaged, or unused books, and I apply the same principle to my writing. I like to whittle down my writing until every word left is, ideally, necessary and working at maximum strength. I find it more difficult to add details than delete them.
While you are working on your small moment, you may find you want to fictionalize it. That’s fine. If you share your work, just make clear to your readers whether it is fiction or nonfiction. However you choose to develop your small moment, keep working on it until you are satisfied with the results.