How to understand the USDA Demand/Supply report ? Need you help .. 
Have couple questions about the Wheat Report


M Acres stands for ? Million acres ?
Yield Bu/Acre , can anybody explain this calculation ? 
Stocks use ratio % , how the calculation works ?
M Acres is million acres, as you suggest
Bu is bushel, in theory a volume of 8 US dry gallons, but apparently for wheat at 13.5% moisture it represents a weight 60 pounds.  Bu/Acre is therefore an average yield: with some minor rounding $\frac{2309}{43.9}\approx 52.7$ in the first column
Stocks/Use ratio seems to be the stocks at the end of the period divided by the total use (domestic and exports) in the period so in the first column $\frac{1181}{2222}\approx 53.2\%$