Items cut or copied to the clipboard (even from other circuits) can be pasted into the circuit currently being edited. To do so, move the cursor to an open area of the circuit and click the right mouse button. A menu will appear with paste as one of the options. Pick that option. The menu will disappear, the items on the clipboard will appear, ready to be placed.
You can also type the ctrl-V key to paste the contents of the clipboard as long as the cursor is somewhere in the circuit editing area.