So there's three things you always should check first off when you are starting a scenario with the first being a survey of your forces, the next being your relationship with the other nations, and finally, getting your economy going.
Since I prefer to focus on the military aspect of the game, my personal preference is to not have to deal with commodities so that is the main reason why I play on the simple economy. Others like the more detailed economy of the original CoG which I can assure you has been kept in and improved and is now known as the 'advanced' economy.
So for the simple economy, the economy screen is very simple to use. Naturally. My main economic levers on this screen are military readiness and draft size. Both of those directly affect my income.
Now for those unfamiliar with the game, military readiness affects the maximum size an individual division can be. The basic unit of strength, the division is normally 10k men for inf/cav and 3k for artillery. If I set military readiness down to 90%, well then my divisions can only be filled to 9k and 2700 artillery. Makes them weaker but saves you money!
Draft size is fairly self explanatory though the exact mechanics are a bit more difficult to explain. Suffice it to say, each draft point adds a certain number of men to the draft pool and costs 15 money.
Other items that affect income in the simple economy is upkeep (your primary expense by a large margin usually), treaty income or expense, and merchants. Oh and colonial income but Poland doesn't have any colonies.
Ok, so that got a little long-winded there but this is a beginners AAR. My moves on this screen were to leave readiness at 100% and increase my draft size to 4. With these changes I expect to get 73 profit next turn (this isn't exact for a number of reasons).