There are a couple of tutorials out there on the internet, 15 minutes googling will give you enough results I guess.
Making the computer boot from the floppy is pretty easy: just place a 512 byte big piece of assembly on the first sector of your floppy.
When your piece of assembly code is bigger than 512 byte, you'll have to load that piece into the memory by hand - the BIOS won't do it for you. For an explanation how to do this, use Google, because I don't know how to read from disk in 16 bit mode

. The handiest is to put the extra piece of assembly on e.g. the 2nd sector, but note you won't be able to use a filesystem anymore.