Connect a record player to a computer. There are several ways to do this. If you have a turntable with USB outputs, use a USB cable to connect the turntable to your computer. If you don't, connect your turntable to a sound system and then run a cable from the headphone output of the sound system to the line-in port of your computer's sound card.
Test various volume levels from the sound system to determine the best input levels for the computer.
You can also use specialized software to "clean up" the sound from the vinyl record and reduce or eliminate any pops or cracks from the old record. This step isn't necessary, but it can be useful if your records have been played a lot.
Play your favorite songs while recording the music on the computer. There are many software programs that will help you record and edit music on your computer, including the free program Audacity, an open source program available free on the Internet. This step will be time consuming--you'll have to record each song as its playing and then convert it to an MP3 file.
Convert the file format of the digital audio file to MP3. Use any of the audio file conversion programs available to create the MP3 file. Once the file is in this format, it can be transferred to portable music devices.