What economics is all about?

Today many people consider economics a difficult field, because economics is the study of the utilization and distribution of scarce resources. Scarcity arises when there is not enough of something. Prior to the industrial revolution of the 18th century, there was enough clean air and pure water everywher. Everyone was able to use air and water as much as they liked without there being an insufficient amount for others. So we say that air and water are free goods. And they can be freely utilized without cost by everyone. Concerning clothes and food, cars and houses, things are different. If society wishes to increase production for example of cars, there will be less resources left for production for ezample of houses. When more of one thing leads to less of another one, we are dealing with economic goods. So we have to talk about some significant object: what is an economic decision and economical wealth of nations in a market economy and in a planned economy? Why it is important to measure alternatives against one another? What should be produced and how should the resulting goods be distributed?