keytab-lilo is a program which compiles keytable definitions (in the format specified in keytables(5)) into a format which can be used by lilo(8) to set the keyboard type when booting [using the keytable parameter in /etc/lilo.conf].
kbd_layout should be the name of a map file which specifies the desired keyboard layout. This file may be a gzip(1) compressed map. If no file extension is given, .map.gz is assumed. If the full pathname is not specified, /usr/share/keymaps/ is assumed.
Since lilo essentially needs to know the differences between the BIOS keyboard mapping and the one you require, the default_layout file should contain a keytables(5) file for the BIOS default mapping. If no default_layout file is specified, us.map.gz is used.
keytab-lilo writes the output translation table as a binary string to standard output, so you should redirect it to a suitable file. lilo has no particular restrictions on the name of keyboard translation files, but the suggested naming convention and location is /boot/mapping.ktl (where .ktl stands for "Keyboard Table for Lilo").
This is the most common form of invocation; it simply compiles the given map file (in this case dvorak) and puts the result in /boot/dvorak.ktl.
lilo comes with extensive documentation; this can be found in /usr/share/doc/lilo/ on Debian systems.