Every country has an Industrial Base. As the name suggests, it is your capacity to produce. Industrial Base is divided into two parts: The private sector and the public sector. They are both worked by your population. The private sector is the amount of your industrial base owned by private individuals in your population seeking to make a profit. It gets money going and is what gives you a domestic monetary income when taxes are applied. The public sector is the amount of your industrial base owned by the government. This portion of industry doesn't contribute to monetary gain directly (see: trade) but is more efficient, so increases your overall capacity to produce.
The differences between the two grow more than that. The private sector seeks to expand. When all variables allow it, the private sector can grow, thus increasing your industrial capacity. Meanwhile, the public sector will only grow as much as you want it to. Both can shrink if you neglect them. They may decline due to low resources, embargoes, bad stability, the works.
How much of your industrial base your country can use is determined by resources, infrastructure, and stability. If any of these get low, you will find your industry will collapse.
Resources are what's needed to produce materials in any industry. You'll need a certain amount of resources per unit of industrial base to run it. Note that resources are used in other parts of economic management, so dedicating all resources to have the largest industry possible isn't necessarily a good idea.
Infrastructure is basically how developed your country is. This rating goes from 1%-100%, and is basically multiplied directly to your industrial base to give you your industrial capacity. To get what you pay for in industrial base, infrastructure has to be at least 75% developed. Going higher will yield industrial benefits that won't require resources to run, increases resource gain, and would set a minimum stability rating that your country won't be able to go lower than so long as it's maintained. However, Infrastructure decays at a dynamic rate per turn and requires a mix of industrial capacity, monetary income, and resources to raise. It isn't raised by a static number based on how much of these you invest; you give a broad plan (the more detail the better), I'll put a price tag on it (combination of funding, resource allotment, and industrial dedication), and your infrastructure could go up by a varying amount dependent on how much of your economy and effort you put into it. Investments into infrastructure is a gamble; it isn't guaranteed to automatically increase it by 20% or something. There is a chance that your public sector can donate some assets to increasing infrastructure, as well.
Stability is your population's approval of you. It controls both how willing your people are to work and how much they are willing to revolt. A bad stability could lower your industrial capacity by as much as 75%. Stability can only be raised indirectly; good management, events, and similar can raise it, and the opposite of these can lower it.
Monetary income is obtained by taxing your public sector and trading. Money is used to find scientific endeavors, infrastructure projects, fund your military, trade with others, or fund your private sector in an attempt to stimulate economic expansion.
