The writing is cuneiform script (https://en.wikipedia.org/wiki/Cuneiform_script), they were created by a wedge on wet clay. I guess our writing would appear as peculiar to ancient eyes :-)

For a general and short introduction to cuneiform I would suggest http://www.amazon.com/Cuneiform-Reading-Past-C-Walker/dp/052... (other books in the Reading The Past series are excellent, too).

Or, if you're interested in other type of ancient writing in general, there's a nice Mayan Hieroglyph workbook online (pdf: http://www.famsi.org/mayawriting/hopkins/MayaGlyphWritingWrk...). It's a great way to waste an afternoon!