This list box lists all the signals of the outgoing GUI element; i.e., the element where you started to drag the mouse. Click on one of the signals to select it; this is the signal part of the connection.
Slots
This list box lists all the slots of the incoming GUI element; i.e., the element over which you released the mouse button. Click on one of the slots to make a connection between the outgoing and the incoming GUI elements. Be careful: By just clicking on a slot, you make the connection clicking does not just select the slot. However, you can always remove a connection later.
Connections
This list box shows all connections that already exist between the outgoing and the incoming GUI element. For each connection, the outgoing GUI elements, the signal name, the incoming GUI element, and the slot name are listed.
Connect
Click on this button to make a connection between the selected signal and the selected slot. Since clicking on a slot already makes the connection, you only need this button if you operate the dialog from the keyboard.
Edit Slots
When you select an already existing connection, this button is enabled and lets you edit the connection.
Disconnect
Removes the connection that is currently selected in the Connections list box.