Tough question to answer, since economists don't fully understand economics yet either, and still get it wrong (how many professional economists besides Roubini foresaw and warned of the financial crisis again?).

Some of the most important bits of foundational knowledge I've accumulated over the years:

1. The Industrial Revolution demonstrated to humanity that wealth could be created from thin air, on a large scale, and hence civilizations had an alternative to stealing it from each other. There are basically two ways of creating wealth:

-1) Harvest raw materials, apply labor, capital, and innovation to convert them into finished products worth more than the sum of their parts. The diff between what it cost to make the product and what you sell it for is the wealth you've created out of thin air (more commonly known as profit). It's why manufacturing is important.

We used to take hundreds of dollars worth of wood and iron and turn it into thousands of dollars worth of sailing ships. Now we take hundreds of millions of dollars worth of sand, aluminum, and copper and turn it billions of dollars worth of microchips.

-2) Provide a service that saves other people time and/or money. Time & money = wealth. With the time/money saved, they can either do more of #1 or #2, invest it, spend it in leisure, or whatever else is of value. More commonly known as specialization.

Most things are combinations of the two - products that save time or money (web apps, cars, etc.), or services that reduce the cost of #1 or increase its final value.

2. In a fiat currency system, the underlying of everything is interest rates, and the underlying of interest rates is the risk-free rate of return. If you only watch one single data point, the risk-free rate is the most important. When it moves, everything moves (since all other interest rates are indexed off of it). Normally the risk-free rate is considered to be US Treasuries, but over the past few years there's been thought amongst some actuaries, economists, traders, etc. whether it's not something else, like a composite of US Treasuries and LIBOR, or something else. But just be aware that there is a concept of a baseline interest rate upon which all other interest rates in the economy are indexed on, and even tiny movements in the baseline rate have major ramifications for the entire rest of the economy.

3. Incentives matter. One of the things that all economists across all schools of thought agree on. One good article: http://economix.blogs.nytimes.com/2009/09/09/what-weve-learn.... Plenty more if you google the phrase.

4. Fractional reserve banking. Many people misunderstand how this works, so I'll preface by saying that individual banks cannot create money. Eg, an individual bank cannot loan out more than it has in deposits. If a bank has $100 in deposits, and the Federal Reserve sets the reserve ratio at 10%, the bank must keep 10% in reserve, eg it cannot loan out more than $90 of its $100. But, the banking system can essentially create money, or multiply it, based on the fractional reserve ratio and the money multiplier. Wikipedia has a good table that demonstrates how this works: http://en.wikipedia.org/wiki/Money_multiplier#Table

4. On a meta level, don't subscribe to one economic school or another, rather learn and understand them all, where and why they disagree, but don't get emotionally invested in any one of them. I see lots of Austrians in this thread and a Keynesian or two. Listen and understand, don't believe. Economics is the study of one of the most complex, dynamic, and intractable systems we know of, and no school has it completely right yet, all are subject to further revision.

5. In that vein, read Benoit Mandelbrot's The (Mis)Behavior of Markets for a good discourse on why economics is so difficult and intractable. http://www.bearcave.com/bookrev/misbehavior_of_markets.html

6. Also read Charlie Munger's Harvard Commencement speech, "On the Psychology of Human Misjudgement", for a reminder of why not to get emotionally invested in one school of econ, or worldview, or religion for that matter. https://duckduckgo.com/?q=munger%20psychology%20of%20human%2...

I can think of more, but that's enough for now, hope it helps a little.