After you build a VI front panel and block diagram, build the icon and the connector pane so you can use the VI as a subVI. Every VI displays an icon in the upper-right corner of the front panel and block diagram windows. An icon is a graphical representation of a VI. It can contain text, images, or a combination of both. If you use a VI as a subVI, the icon identifies the subVI when it is called from the block diagram of another VI. (Windows) Windows Explorer also uses the icon to identify the .vi file if you enable this feature.
You also need to build a connector pane to use the VI as a subVI. The connector pane is a set of terminals that corresponds to the controls and indicators of that VI, similar to the parameter list of a function call in text-based programming languages. The connector pane defines the inputs and outputs you can wire to the VI so you can use it as a subVI. A connector pane receives data at its input terminals and passes the data to the block diagram code through the front panel controls or receives the results at its output terminals from the front panel indicators.
To view the connector pane for a VI, right-click the VI icon and select Show Connector from the shortcut menu.