How do I move, copy or delete a block?

Hover the block and use its toolbar: ↑ and ↓ to move, ⧉ to duplicate, ✕ to delete. You can also drag blocks into order in the "Blocks" panel.

With a block selected and no text being edited, Backspace or Delete removes it. Deleted something by mistake? Undo (⌘Z / Ctrl+Z) brings it back.