The connection tool activates automatically and the cross icon appears when you hover your mouse cursor over the port icon. When the cross icon appears, left-click and drag and drop to the target.
For pins, the Connection tool activates when you hover over a pin icon or pin name.
For nets, the Connections tool activates when you hover your mouse cursor over any part of the net.
The connection tool does not activate when you hover over pins, ports, or nets in the following cases:
For the hierarchy views.
Inside the configurator window.
When "Zoom to Selected Area" mode is activated.
When "Add Note" mode is activated.