Each input field can have a Description, a longer note shown behind a help icon next to the field. Where the Title is the field's short label, the Description is room for extra guidance, like "Use your landscape logo" or "Keep it under 40 characters".
Set it in the field's editor, in the Description box. Your users then see a help icon next to the field and read the note when they hover over it.
The Description is optional: leave it empty and no help icon appears. For standalone guidance that is not tied to a single field, use an Instruction field instead.