Open Disk Management, right-click your drive, and select Format to start erasing it. Choose NTFS for the file system and uncheck quick format to ensure a complete format. Formatting deletes data but doesn't fully erase it, so use additional methods for a complete data wipe.
Formatting your computer means erasing all the data on the hard drive (s) and then reinstalling Windows or macOS for a fresh start. This can be useful if your computer isn't working right or you plan to sell it and don't want to risk someone recovering your data.