The info icons

A small circled i beside a label explains it. Hover it, or move to it with the keyboard, and a short note opens; move away and it closes.

The screens keep their own wording short for this reason: once you know what a field does you do not need to read about it again. The icon is there for the times you do. Clicking away or pressing Esc closes it. Screen readers read the explanation along with the label, so nothing is hidden from them.

Each note is the short form of a page in this guide. Where a note ends with a topic name, that page has the whole story.