Next, you need to create a file that represents a hard disk drive from the perspective of a VM. In a CLI (command line interface, AKA DOS-box), navigate so that the current working directory is the directory of QEMU executables.
Next, use the qemu-img program as follows:
This creates a qcow2 file that represents a hard disk drive that is up to 512MB. This should be sufficient for most programming classes. You can specify a larger size, but make sure you have the space available on the thumb drive or external hard disk drive.
A qcow2 file starts small, and grows as it needs to. This means that if you only use 100MB, then the file is about 100MB.