It should be remembered that these instructions are intended to show how to re-format your hard disk to F+ format to allow you to take advantage of long filenames and greater than 77 files in a directory.
Remember also that if you reformat your default drive :4 without having backed it up first, you will lose all your data. You can of course format drive :5 without affecting drive :4.
The following four pages are scanned from the RISC OS 4 Upgrade Manual which gives a good simple account of how to use HForm.
Bare text of the pages