You wish to reboot a target computer. Also an installation may require a reboot but letting the installation media reboot the target can cause problems.
Use the Reboot Step. It allows a time to be set and also displays a message to the user so you can give an explanation and a warning of how long they have to save their work. This can also be used with a check in the "Shutdown Only" box for circumstances like preparing for power loss, with that box checked it will do a shutdown instead of rebooting.
Lex provides an introduction to the Reboot Step, just one of the many steps you can use in creating or editing a package.
This step is important to resolve issues for packages that require rebooting to complete the installation. If the installation media is allowed to reboot the target it can cause a connection to drop with the PDQ Deploy and result in a failed or reported failed deployment. Make sure the proper reboot prevention is happening by the appropriate parameters and this step is used to ensure proper success in your deployments and their output logs.