Activating Auto-connection turns on the Automatic Connection mode. An 'A', displayed on the left of the information bar, indicates that 'Automatic Connection' mode is turned on.
Hint
You can also turn the 'Auto-connection mode On/Off with function key <F10>
When a component is placed with 'Auto-connection active, it will be automatically connected to the component above or below it (or to the right or left depending on the mode selected). In addition, if a node is drawn, a connection line will also be drawn to a component directly above or below it. Existing connection lines will be opened automatically. Automatic connection and opening of connection lines also works with the UNDO, REDO, Repeat and Copy commands. Opened lines will also be closed again if Delete, UNDO or REDO is used.