1) What to produce:
This problem is what should the economy produce in order to satisfy consumer wants (as seen by demand curves) as best as possible using the limited resources available. If a country produces goods in a way that maximises consumer satisfaction then the economy is allocatively efficient.
2) How to produce:
This problem is how to combine production inputs to produce the goods decided in problem 1 as most efficiently as possible. An economy achieves productive efficiency if it produces goods using the least resources possible. A productively effiecient economy is represented by an economy that is able to produce a combination of goods on the actual curve of the PPF.
3) For whom to produce:
Should the economy produce goods targetted towards those who have high incomes or those who have low incomes. What sort of demographic group should the goods in the economy that are produced be targetted towards? If the economy is addresses this problem then it has reached preto efficiency or pareto optimality.
If all three problems are addressed at any one time then the economy has achieved static efficiency. If the economy achieves static efficiency over a period of time then it is dynamically efficient.
All these problems are focused around the problem of unlimited wants and limited resources. Where resources are the fators of production (such as labor, capital, technology, land..) which are used to produce the products that satisy the wants.
Source:
My first ever economics lesson many years ago.