Connector panes are used in subVI's to pass parameters to and from the subVI. The connector pane is selected by right clicking on the VI icon in the upper right hand corner of your VI, then choosing the Show Connector menu item.
Right-click again on the VI icon and choose a pattern for you subVI's connector pane.
It is considered good practice to choose a pattern that has more inputs/outputs than you need when writing the VI so that new inputs or outputs can be added without changing the connector pane and causing the VI's that link to your subVI to recompile.
The 4x2x2x4 pattern highlighted above is the most commonly used for NI primitives. In LabView 8 and above the connector pane is defaulted to the 4x2x2x4 pattern.