Typically as mp3 files compressed to 128kBit/sec.
Generally I only fit 85-90 songs on each CD-R
because I use much less compression (a higher bitrate)
Commercial pressed cd's use a format refered to as CDDA.
"ripping" those songs to your computer as uncompressed files
results in a wav/pcm file.
Compressing either at the same time the audio data is extracted from the CD or as a seperate operation of the files after they are already on your HDD (Hard Disc Drive)
Does your playback device support mp3 playback?