file manager to download are "mc" (midnight commander), "emelfm2" and "gpe file manager". but i would go for "mc".

they are available in the extras or testing or devel repository.
if you want to know where they are... search here: http://maemo.org/packages/

mhm... i think the best way is to use the man-pages or --help or google for commands

edit: too slow ^^
but ssh is also a nice way for doing that.
and the best about this is:
when the system gets screwed up (because something dumb happens xD) you can ssh in and may try to repair it before you have to reflash it.