At 38 degrees, 12 psi once you reach equilibrium (2-3 weeks without any agitation) you'll have 2.57 volumes of CO2 in the beer. Everything on the chart is labelled pretty well?
The colors are just to give you an approximate carbonation range (see the bottom) and the top is labelled PSI. If you're using the "set and forget" method you just want to leave it at that pressure and not change it. Should be mostly carbonated after 2 weeks.