Obtain a USB-based turntable that can be attached directly to your Mac via the Universal Serial Bus (USB) connection. There are many different brands of USB turntables available on the market, so take some time to research them before purchasing.
Install the software that accompanies the USB turntable, following all directions that accompany the program. This software will allow you to take an audio signal coming into your computer and convert it directly into an MP3 digital audio file. Once the software is installed, start the program so you can begin using it.
Connect the turntable to your computer using the included USB cable, then begin playing a record. Follow all instructions that accompany your USB turntable for turning the analog audio signal into an MP3 digital audio file.
Use the software that accompanies the turntable to make each song on the vinyl record album into a separate digital audio track. Tag each track with information such as the name of the artist, the song title, and the album from which it came.
Purchase a turntable pre-amplifier that can boost the line signal output of your analog record player, then hook the turntable up to the pre-amp using the instructions that come with the equipment. This will make sure the signal coming out of the turntable will be of a level sufficient for recording.
Connect the pre-amp output to the audio input of your Mac. Typically, the output from a pre-amp will be two RCA jacks---one each for the left and right portions of the stereo signal---so you will need a cable that has two RCA plugs on one end and a 1/8-inch stereo plug that can be plugged into your computer on the other.
Obtain software that will record audio coming into your Mac via the audio input jack and convert it into MP3 digital audio files. A popular low-cost option is Roxio's CD Spin Doctor (see References). Another choice is Garageband, which comes pre-installed on all Mac machines as part of the iLife software suite.
Follow the instructions that come with the audio recording software to convert the analog audio signal coming into your computer via the turntable and make it into an MP3 digital audio file.
Purchase an all-in-one Vinyl-to-MP3 conversion unit. These resemble a stand-alone stereo system with built-in turntable that can convert the analog signal created by the vinyl record into a digital signal that can be burned to a compact disc. No computer is needed for these systems.
Place your vinyl record on the turntable of the all-in-one system, then place a blank CD-R or CD+R into the tray of the CD burner. Follow the instructions that come with the unit to finish the recording process.
Convert the newly-burned CD tracks into MP3 audio files by ripping the tracks to your computer hard drive using iTunes.