While it has long been possible to store music on a computer hard drive, it has only been relatively recently (since about 1998) that it gained popularity. The change was brought about by a couple of different factors. People started applying compression techniques from digital video to music, which reduced the size of a five minute song from a 45 megabyte WAV file to a 5 megabyte mp3 file. At the same time, hard drives were getting cheaper — it became practical to store the music files on the computer. And finally, the files were small enough to send to another person over even a modest Internet connection. Of course the biggest factor in the rise in popularity of digital music was Napster. Napster allowed people to download music from people they didn’t know. It allowed people on the Internet to get mp3s, even if they didn’t know how to create them. Once people started to create their collections of mp3s, the inevitable changes in consumer electronics occurred: companies released portable mp3 players, and CD players are able to read CDs with mp3 files on them.
There are a number of tools out there that make it easy to create mp3s. For example, MusicMatch is a popular program that comes pre-installed on many computers which will allow one to simply pop in a CD and choose an option to copy the audio tracks as mp3s. To get the best results in creating mp3s, though, one should use a combination of two pieces of freely available programs: EAC and LAME. Creating an mp3 is a two step process: 1) copying the music off of the CD and 2) compressing the music into an mp3. EAC is a tool for extracting the music off of the CD (also known as "ripping the CD"). LAME can then compress the extracted music into an mp3 file. Since these two tools are often used together, EAC has been built to be able to directly create the mp3 file by using LAME under the covers. The combination of EAC and LAME produces the best results because EAC is essentially one of the best pieces of software out there for extracting audio tracks — it includes sophisticated error correction logic, which enables the audio to be copied correctly even if the disc is scratched. LAME is one of the best freely available mp3 compression tools out there. It’s fast and it produces good results.
For more information, take a look at the FAQs from Anandtech on Ripping CDs and Encoding MP3s.