You get a financial report from each region every month (it's on no set day, when they get to it, they get to it). If you take in $250 or more from each region (after Apple takes their 30%) then you get paid. So if you had a 99 cent app, you'd need to sell ~375 of that app before you'd get paid out.
But as stated above, read through all the docs, it's clearly explained in the agreement you signed.