You might want to go through the MA 105 document on this site.
http://home.pct.edu/~jmather/content/DSG322/inventor_surface_tutorials.htm
also,
http://www.mcadforums.com/forums/viewtopic.php?t=8698
and,
I assume you know about http://engineersrule.org there is a complete curriculum on that site. I'm not sure what is available to students as compared to that available to faculty. Ask your professor to download the pdf curriculum and sample files if you can't find them.
and finally,
Go through the Help>Tutorials, there are a couple on Design Accelerators that would have indicated to you to start with an Assembly file. (Save the file before starting one of the Design Accelerators.)
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