Throwing up will not reduce your current blood alcohol percentage, but if there is unabsorbed alcohol in your stomach, throwing up can prevent your blood alcohol percentage from increasing through additional absorption. Metabolism and time is the only way to reduce your blood alcohol percentage.
It means it's 40% alcohol. The proof number is twice the percentage of alcohol. Proof is a system of measuring the alcohol percentage where 200 is 100% alcohol. So 80 proof is 40% pure alcohol by volume.