Most of them you can make out yourself. Mfg. goods is shields per turn from all cities, GNP is gold, approval rating is a ratio of happy people to content/unhappy people, military service is a ratio of population to military units, etc. But again, we don't keep these mathematical formulas in our heads, they're out there on the forum and the rest of the internet, if you take the time to look for them.
Also, the demographics screen serves very little practical purpose in the game besides eye-candy. If you have diplomatic ties to the AI you can kind of use it for espionage, to estimate their rough economic strength, but it only shows the strongest AI for comparison in each category. But still, you can see how much gold and shields they make per turn, if their science and population infrastructure in place (literacy rates rise with more libraries and universities, disease % is lowered by granaries, aqueducts and technologies like medicine, and upped by pollution), etc.
For the last time, do what all other Civ I nerds do here when they first come and read the forum from start to finish. That is, if you really want to know all of these things about the game that you're constantly asking.