Fair Isle Question

Ive a tiny amount of fair aisle knitting but the pattern I worked on came with a legend telling me what the symbols meant. I want to knit this little purse after watching the video but I have no idea what the x’s o’s and - means and what do the blank boxes mean? Can anyone help? Thanks
http://www.philosopherswool.com/Pages/SamplerPurse.htm

The empty boxes are your background color. The X’s are one contrasting color, and the O’s are another contrasting color.

I always take an X and O chart, and color it in…

use colored pencils (my favorite) or color hi-lighters (that you can see through), or even water color paint or water color markers (again, like hi lighters, clear color)–regular markers are too opaque. (for my taste–but you might like them)

i like pencils, cause they come in the largest range of colors, and i like to use colors close to the actual yarn color…

make a key for your self if needed -if the pattern has 3 shades of blue, i often make Lt blue, grey, dark blue–instead of straining with Lt, medium and dark pencil colors.

this preplaning pays off… an hour spent fixing up the chart often is many hours saved (from frogging)