The system image is read-only, so even if it's screwed up with bad commands run as root - it will return to the default once the system is rebooted. But the home directory is read-write so any files you save there will persist after a reboot.

# You'll need an ADATA UV128/32GB USB stick. You can use a different one but it has to be at least 31,037,849,600 bytes in size. A USB3 stick is highly recommended, even if you're using it in a USB2 port (the flash inside is faster).