How can I download music onto iPhone

For those of us who don't know yet. Could someone please post a guide on how to download music onto iPhone accessibly? If I have music on flash discs how can I transfer it? What are some good sites to download music online to a pc and maybe then to an iDevice? Are some of theese sites safe against viruses? What are some good apps on the iPhone that allow you to download music? If you know of any please also say proceedures on how to download music onto both or either iDevice and computer. I have Jaws12 so please say if there are any limits to downloading music from a computer. Thanks