Two kinds of reusable structure, in two places.
Card templates
Templates in the sidebar holds card templates: a name plus a markdown body that becomes the card's description when applied. Build one for anything you write out repeatedly: a bug report with its repro steps, a client brief, a weekly review, a packing list.
Create and edit them from the Templates page; apply them when creating a card. The body is ordinary markdown, so checklists inside a template arrive as real, tickable task lists.
Board presets
When you create a board, the dialog offers column presets: the classic To Do / In Progress / Done, and shapes for common jobs. A preset only decides the starting columns; nothing stops you renaming or rearranging after.
Checklist templates
Standalone checklists have their own template system, covered in Planner, Today, and Calendar: save any checklist as a template and re-run it fresh each time, which is the right shape for packing lists and pre-flight routines.
Where the boundaries are
Templates are per workspace. There is no cross-workspace template library yet; if you need the same template in two workspaces, create it in both.