You don't need to create a checkbox. This control already exists in the System palette. It's just a Boolean control, so you can easily check its state and display a dialog if it's true. For example, you can use the Display Message to User Express VI to display the message. It has an "enable" input that you can wire to the checkbox control.
To learn more about LabVIEW it is recommended that you go through the tutorial(s) and look over the material in the NI Developer Zone's Learning Center which provides links to other materials and other tutorials. You can also take the online courses for free.
