When you buy music online, the files you download are generally MP3s. Unless your car stereo specifies that it will play an MP3, MP3 music files burnt onto a CD won't play in your car's stereo. In some instances, because of media protection encryption, burnt MP3s auto convert to MP4 and will not play in your car stereo. Car stereos usually will only play "Audio" files. Your first task is to make sure you have the authorisation and license to convert the music on your computer. Usually, if you bought it, you have this authorisation.
Purchase a blank "Audio" or "Music" CD-R. Buying a "Data" CD-R to burn MP3s can leave you with a CD that may only work in another computer. Burning music to a Data CD-RW will render the same effect. Often Data CD-R and Data CD-RW simply "copy" your MP3 format to the disk or burn to a MP4 format, which is not always compatible with a car stereo system. Purchasing and using a "Music" or "Audio" CD-R that is specifically designed to burn music increases your chances that the CD will work in your car stereo system.
Load the empty Audio CD-R into the CD/DVD drive of your computer. Your default music player will load and notify you that your computer is reading an empty disk. If you are using iTunes, it will tell you in a pop-up window that you have inserted a blank CD or DVD and ask you if you would like to burn a playlist. Click "OK." You won't see the blank CD in the navigation area, so dragging and dropping music to the CD is not possible.
Select a playlist you have built from the list of playlists. If you have not built a playlist, do it now. Go to "FILE > New Playlist." A new playlist will appear. Name it and proceed to drag music from your music library to this playlist. Usually a blank Audio CD-R will hold about 16 songs. At the bottom of the iTunes window (assuming you are using iTunes), you'll notice the amount of space your list takes up on a disk. This will let you know how many songs to add.
Highlight the list with your curser once you finish adding songs. Right click your mouse. The option to Burn Playlist to Disc will appear in a pop up window on a list of other options. Select the "Burn Playlist to Disc" option.
Select "Audio CD" as the Disc Format when the second pop-up window appears. Within this window you can also adjust the gap between songs and regulate the sound. CD players in some vehicles can display information stored on CDs; select Include CD Text in this same pop up window to use this option.
Click the burn button at the bottom of the pop-up window after you've personalised your audio choices. The process should auto start. When it is complete, the Audio CD should auto eject from your computer and be ready to play in your car stereo system depending on your car stereo. It is possible that your car stereo may only play a professionally manufactured music CD.
About your car stereo system: Always refer to your car stereo system guide and warranty information prior to using homemade CDs in the system. About your MP3 files: If you are not authorised or have the license to convert or burn music files that are on your computer, during the burning process these songs will not burn and will be missing from your finished CD.