"To reboot the device" means to turn it off and then turn it back on again. This helps fix any issues or problems the device might be experiencing. It's like giving it a fresh start. Full definition
Wait for the installation process to complete and after you can reboot the device in normal mode. (android.gs)
It is recommended that once you've installed and set it as your home launcher, you should let it «settle» for a little bit, then reboot your device. (android.gadgethacks.com)
At this point, simply reboot your device so the changes will take effect. (android.gadgethacks.com)