How to Count Items On Sales Order by Week?

I'm trying to create my first report…

I would like to count how many of a each Item shows up on Sales Orders each week. 

Something Like:

                       Week 1       Week 2        Week 3

Item 1
Item 2
Item 3
Total

I assume this would be a Transaction Report, filtered by "Sales Orders".  What is the variable used to identify the Quantity Field on a Sales Order Line Item?

I must be overlooking something simple.  I can't seem to make this work.

I would also prefer a graph if that is possible. 

-reed