I'm by far not an expert ,but from what I do know:
Every bitcoin released must use computing power to enter circulation. They are hidden in long strings of encryption: thus cyrpto-currencay. Plus using your computer on the serve, helps with transaction, and you might fraction of transaction fees. They come from the bitcoin server, and who ever created the p2p network.
As more bitcoins enter circulation, the more difficult the encryptions become, which make them more rare to mine and price raise. Only 21m can be mined.
The argument about bitcoin, is nothing is backing it. Then again, nothing is backing our dollar - the mint regular just prints money out of thin air and throws it in circulation. I'm not really sure what gives it worth, just like I'm not exactly sure what gives our modern day dollar worth.