How to format powerbook 1400

I have a powerbook 1400cs with only a floppy drive. I am new to Mac computers. I only have floppys built for Windows PC's. I would like to sell this laptop but I either need to format the hard drive (use a utility to permanently erase everything) or just erase all personal info off the drive (permanently). I don't know how to do either of these.

If I format the drive, I have no way to put an operation system on it.

Also if I could get a pdf manual of OS 8.1, that could help.

Specs:

Mac OS 8.1
117MHz CPU PowerPC 603e
Built in memory - 28mb
RAM doubled to 56mb
Machine ID - 310

Sorry for the wrong post. I only thought to format to erase all personal info. But I'd rather just delete it only I don't know Mac's so I don't know how or where to get rid of the info.