manual steps to install linux on external drive from ISO file AND without booting into it?

manual steps to install linux on external drive from ISO file AND without
booting into it?

I would like to know what the manual steps are to replicate the operation
of unetbootin linux utility.
That is to say - how to manually install (and by word manually I really
mean using the command-line and basic linux commands) a linux system on an
external drive / stick from an ISO file sitting at another running linux
system.
In my case I am running Fedora 19 and I want to install another
distribution (regardless of which exactly) on a connected stick / drive.
I would like to learn and understand my linux better. There are many
tutorials on the net but all of those I have found EITHER resort to using
some installation utility OR boot from the drive to continue the
installation once GRUB is on and iso file tranferred there.