OK, suppose you have a basic Mineral Miner I that mines at a rate of 800 minerals per turn. That's really only the rate you'd get on a 100% mineral planet, though - to get the real production rate, you have to multiply the miner's rating by the planet value (and a few other modifiers). So on a 150% planet (the maximum you can normally find) your 800-mineral miner would produce 1200 minerals... but on a 5% planet, it would only produce a puny 40 minerals. The same goes for organics farms and radioactives extractors, except they use the organics and radioactives values respectively.
If you want to know about the other modifiers, basically, you also get a bonus if your population is happy or jubilant, a penalty if they are angry or unhappy, no resources at all if they are rioting, various bonuses for different amounts of population on the planet, and special modifiers from facilities and racial traits.
Does that help?
