Please read the author's introduction: "An Introduction to Display Editing with Vi" http://www.verticalsysadmin.com/vi/vi_editor__bill_joy.pdf

I also recommend the O'Reilly "Learning the vi and vim editors" book, http://shop.oreilly.com/product/9780596529833.do and my own course on vi basics, http://www.verticalsysadmin.com/vi.htm