In its current state, the Econ model for D5 isn't that much of a sub-game yet.  But an awful lot of the underlying work for the final model has been done, and hopefully you, the player, will be able to see the foundation that will allow us to have a low-micromanagement high-fun civ game.  What the economy can do so far, is build military units, and the economic infrastructure itself.  By checking out the Econ model you can see some of the basic ways that economic growth will happen in Clash, and be able to give some insight as to the type of final economic interface that will be most valuable for the player to have.  I have to say upfront that the present interface is in no way intended to be something that goes into the game!  What it does allow you to do is mess around with the Econ system and put it through its paces.
 

The Econ Orders frame

Across the top of the Econ Orders frame you'll see for your civ: the current tax rate (adjustable); income from taxes, money used by spending on government orders, and net income.  For now, there is a limit to the tax rate you can set -- it needs to be below 11%.  That's because your economy is near subsistence, and taxing at any higher rate would result in starvation of your people.  (Even that option will be available to players eventually, but for now the economy handling is being kept simple.)  The total treasury is shown in the Econ Info frame at the upper right.  For now there is no limit on spending money, so your treasury can go far into the negative values without any consequences for the player.

The rest of the Econ Orders frame shows various infrastructure classes (including building of military units, which are handled as infrastructure in Clash) and specifies any building orders related to each class.  The Clash system for handling building stuff has two main parameters: one for how much to spend (% spend -- this is the only type of control you have in most 4x games) and one that characterizes the threshold beyond which you would like to stop spending on the category (ROI Min).  Essentially there are two factors to the interface, how much you want to invest in a given area when you view it as a good opportunity (% spend), and what you define as a good opportunity (ROI Min).  These two factors are the two columns that you can enter numbers into for each type of infrastructure in the Demo 5 Econ interface.  Future interfaces will not require entry of numbers for those players not interested in fine control of the economy.

Let's say you want to push production (=prod = manufactured goods), but only in areas where it will pay off at least within ten turns or so.  You should look down to the "prod kapital" row for an example.  The reason the name of the infrastructure class has kapital in it, is that the infrastructure class covers capital investments in the production sector, like workshops or factories.  For the "prod" sector, orders at start-up are set to use 10% of local taxes as the investment amount with a rate of return needed to invest of 10%.  What the game will do when it gets to the economic orders phase of the turn, is examine your order for every square in your civ, and decide based on your return rate whether to spend up to the amount you allocated (10%).

So let's say in one particular square the taxes you get are 100C.  The Econ model will do a simple rate of return calculation, and find out how much you should invest, up to the 10% (=10C), while still meeting your needed rate of return of 10%.  What the rate of return calculation considers is how much the investment will pay back directly to you, the government, in the future, and what annual rate of return this is equivalent to.  (Right now the rate of return doesn't consider what the people might get out of an investment, only what the govt gets back in the way of increased taxes.) 

This approach allows you to switch on or off investments over your whole civilization with just a few orders.  By adjusting the rate of return you can either invest anywhere it will do the least bit of good (1% rate of return), or invest in places it's fairly advantageous to do so (10% or so) or only cherry-pick the very best places to invest (say 30%+).  If what you really want is money, just set all the local tax percentages to 0, then you will just get your taxes sent directly to the civ treasury.

Getting back to the Econ Orders frame, there are two columns to the right that allow you to monitor how much each order is costing you.  The one that says "Type Cost" shows how much orders of this type, FE prod kapital, cost over the entire civilization.  The second one "This Cost" gives the cost of just the particular order you entered.  The distinction is that you can have orders for increasing production capacity both at the civ level, and at lower levels like regions of your civ (not implemented yet), provinces, or map squares.  So you need a way to distinguish what the order at the civ level is costing, versus what orders at different other levels may be costing.

Now you've got enough information to actually see something happening.  If you look at the cost for your prod kapital order, they'll probably be something like 50 for the "Type Cost" of the order, and 25 for this particular order.  What this means is that there are investments with in your civilization that meet your 10% ROI requirement, and exploiting them will cost your treasury that much.  At this point you should push the end turn button several times, pausing to see how these numbers update as each turn is run.   You'll notice that although there were opportunities for investment that met your criteria on the first turn, after a turn or more the spending in the production investment order category will decrease toward zero.  What's happening, is that the system is doing exactly what it's supposed to, and ignoring your investment order when no good opportunities exist.  And the reason no good opportunities exist, is that you have diminishing returns in the production sector for several reasons: natural resources going into the production sector haven't increased greatly, and production of more manufactured goods relative to everything else has led their prices to decline, etc.  However, if for any of several reasons good opportunities should again appear in the production sector, your order is there ready to kick in.  Opportunities could improve above 10% ROI due to any of several reasons including: adding new underdeveloped areas to your civ, merchants making available cheap new sources of natural resource inputs to production, or if production technology should improve (it doesn't in demo 5).

You can also augment the civ-wide settings at either the provincial, or individual map square level.  It just depends on how interested you are in tweaking the economy! 

Eventually you can enter the cost for a given order (how much money you want to spend) and the system will set an appropriate % spending and ROI to spend that much while doing it in the most effective fashion.  Eventually you will also be able to set tax rates for individual orders.  In this way you can penalize or subsidize various economic activities of your people in ways used in modern mixed economies.  To see more discussion of how these features will work in the final game you can check out the Economic Model II  thread 

The Econ Info Frame that comes up at the same time as the Orders frame shows information on your overall economic status, and the productivity, growth, etc. of the sectors of the economy like farming or resource extraction.

For a detailed record of what is going on in the economy for the selected square, you can read the economy.txt file.  The file is overwritten each time the program is run.