The simplest way to think of the difference between micro economics and macroeconomics is to recall that the prefix "micro" means "small in scope or scale." The prefix "macro" means "broad in scope or scale." When applied to economics, microeconomics refers to studying particular segments or parts of an economy. Macroeconomics applies to studying the economy, economic events, or economic forecasting from a national or global perspective
An example of a microeconomics study is a researcher looking at consumer behavior at a local mall. Another example is a researcher looking at labor shortages in a region. An example of a macroeconomics study is a researcher looking at national consumer behavior trends in malls across the United States. Another example is a researcher is looking at labor shortages in the United States to predict what type of occupations will be needed in the future to keep the economy growing.
You may find either of these two articles of interest: Micro and Macro: The Economic Divide or Macroeconomics Finally Gets Interesting. In the first article, the author discusses why there is a division between microeconomics and macroeconomics. The second article discusses the author's process used in making economic decisions and forecasting. Click on the title with the links to read either article.
The last item you asked about is sunk cost. The sunk cost is money that is spent and unrecoverable in the cost. Usually when a person is discussing sunk cost, they refer to money spent on a project that is becoming so expensive that they will be unable to recover the cost through sale or profit. A modern example is nuclear energy plants where billions of dollars are spent, and the building expense cannot be recaptured through the falling price of selling electric energy to consumers.