An architect or builder can add/manage checklists within an element.
To add checklists to an element, you need first to have created a checklist area (see How do I add/manage content areas within an element?).
Next, ensure you are in edit mode, by clicking the edit mode action button from within the element action bar.
Within the element builder, architects and builders can add a checklist area (or multiple checklist areas) to an element – by clicking on the “add element content areas” action button (“+”) in the element builder action button panel and selecting “Checklist area”. Like all other content areas, they can then be placed (using the blue drag-drop action button) in any position.