The pre Made VIs all have input and output terminals, which can be wired up when the VI is placed in another VI. How can I put these on VIs I create?
In your VI, create a control or an indicator(control for input, indicator for output) and place it like you normally would in your code. Then, on your front panel, right-click the icon of the VI in the top-right corner of the window. Select Show Connector, then click a blank(white) connector. You should see the wire spool cursor appear when you mouse over the connector. After you have selected the connector, click the control or indicator you want to connect it to, and you will be able to connect a wire to the VI from another code.