Installing macOS on a new hard drive can be done using a USB install, install CD, or through Internet Recovery — you will need to have a Wi-Fi connection to be able to do this.nnYou can activate the Internet Recovery by turning on your device and holding down Command+Option+R and using the Disk Utility to format the drive and the use the Reinstall OS X tool to install the macOS.nnWhile Mac devices provide a suitable tool to help users to deal with and fix damaged or corrupted drives or macOS, it may be wiser for you to ask a professional if you are not tech-savvy or you cannot afford to totally lose your important files.