Governments play the normal game with the added restriction of requiring a certain amount of money for each unit (both building and maintaining). The catch is that one center does not provide enough money to buy a new unit. So, you have to get extra money by borrowing it. One way to get money is by borrowing it from other (also poor) governments. The other way is through selling Victory Bonds. So, you will advertise how much money you need (in thousand dollar bonds) and the Creditors will buy these. The way they will buy these is by making bids to Fasces. In their bids, they will specify the bonds they want (country and number) as well as the interest they expect to receive. Fasces will grant them bids based on the lowest interest rates. The governments will then get money, but will also have to pay interest back to investors based on whatever rate they got. The bonds also have a term (I think 5 years) over which they mature. At the end of that term, the governments have to pay back the value of the bond.
For example, let's say you as a government ask for $2000. (It's small for game purposes, but it will work for now). That means that you will sell 2 bonds. Now suppose that there are 3 creditors willing to buy your bonds. Let's call them A, B and C. Creditor A has quite a bit of cash and thinks you're doing pretty well so he's willing to buy both bonds. He tells Fasces this and decides that he'll ask for 7% interest, because he wants one of the lowest rates, but he also wants to make as much money as possible off the investment. Creditor B can only afford one bond from you and he decides that he wants 5% interest. Creditor C also can only afford one bond but wants 10% interest. So Fasces, on your behalf, accepts the lowest 2 bond offers. B has the lowest interest rate so he gets one bond of $1000 at 5% interest. The next lowest is A's rate of 7% so he gets the one remaining bond, even though he asked for two. So, your country has raised $2000. But, at the end of each year, you pay interest. This comes to $50 to B and $70 to C. Then, at the end of the 5 year bond, you pay back your loan. So, $1000 to each B and C. So, for your $2000 you paid the original back as well as paying $120 in interest in each of 5 years. So, you end up paying $2600. But, you probably got more than that out of the conquests financed with your loan.
For more details, read the full rules.