If you didn't like this tutorial, or you want more practice, check out the Programming Historian's guides
for getting starting in Omeka:
http://programminghistorian.org/lessons/up-and-running-with-omeka
or
for creating an exhibit:
http://programminghistorian.org/lessons/creating-an-omeka-exhibit
To get a better grasp on Dublin Core, check out Omeka's guide: https://omeka.org/codex/Working_with_Dublin_Core
as well as
Digital North Carolina's guide (and their multiple examples):
http://www.digitalnc.org/about/participate/describe/
Have a question I didn't answer here? Try Omeka's very comprehensive info page:
To find more Omeka inspiration check out this directory of sites which were built using Omeka: http://omeka.org/codex/Sites_Using_Omeka
Good luck!