Money is Debt

Start from the first YouTube video here and follow the thread to the next ones :)

The total amount of money is linked to the total amount of debt since money is created through debt. But of course not only.

So basically money is now an agreement, a contract between all the people using it. The value of money is fixed by the market or by what everyone thinks is fair at a given time.
And debt is basically a promise made by the borrower to work until he produces, in one way or another, the amount of money he borrowed (plus interest!).
The thing is that bankers lend you money they never had, that does not exist until you create it with you labor.
Money represents work. So the more work been done, the more money you need.

To finish I would say that I am not completely convinced that interests have to increase all the time. To take the example of the US government debt, nothing prevents it to be repaid if the government wanted to do so (of course it would be less money for the economy).