A reminder is "when"; a note is "what": the door code, the filter size, the policy number. It does not go away once you have read it.
In the chat: "note that the garage key is in the blue box". Or in the Notes tab — the field grows to six lines, and a Title (optional) field appears under it.
You need not write a title: a note of several lines is headed by its first line, and a note made in the chat gets a short title right away — in the same request, not a second one.
An important note can be pinned: in the app — "⋮" → Pin, on the website — the ★ by the note. A pinned note stays on top and always shows in full. Long notes are folded to three lines ("Show all"), except the pinned ones and the newest. The order is "Newest first" or "Recently edited first".
In the app — "⋮" or a long press on a note: when it was saved and changed, Edit, Pin, "Also remind me", Listen, archive. On the website you fix a note by simply tapping it.
"Also remind me" — pick a day and an hour, and the note arrives as a reminder while staying where it is. "Stop reminding" removes only the reminder.
In the app the note field has a 🎤: dictated words are added to what you have typed, and you keep the note yourself, with the button. Listen in the note's menu reads out the title and the text.