A selection can be copied to the clipboard using Ctrl+C.
With blocks in your clipboard, you can paste back into the world by hovering over the desired location and pressing Ctrl+V. Pasting like this will initiate a Placement (see below).
The clipboard can be cleared by right-clicking the icon and choosing the 'clear' option. Left-clicking the clipboard opens up the Blueprint Browser.
Placements can be repositioned and rotated using the Gizmo.
Once the placement is in the correct position, you can use Enter or Ctrl+V to confirm it. To cancel a placement, use the Delete key.
Tip: The placement can be rotated clockwise using the Ctrl+R keybind, and can be flipped in the direction of your mouse vector using the Ctrl+F keybind.