Google is your friend. ;-)
http://www.google.com/search?q=ubuntu+start+ocropus&ie=utf-8&oe=utf-8&aq=t&rls=o\
rg.mozilla:en-US:official&client=firefox-a

One search result that might be helpful:
manpages.ubuntu.com/.../ocroscript.1.html

I see from the previous post that OCSopus is a command line utility. I think
you would be much happier with sane. It has a graphical interface and
recognizes virtually all scanners right out of the box. You will find it in
the repositories (not depository), i.e. install with Synaptic or the
Software Manager.