making a cd

I record a cassette tape, export to my desktop, then send to windows media player. after creating a cd, the music is in mp3 format, and i cannot play the cd in my car. my question is how do i change the format to get the cd to play in car

By default Windows Media Player creates “data CDs”. You need to set Windows Media Player to create an “audio CD”. (I don’t use Windows Media Player so I don’t know where that setting is, but it will be in the settings somewhere. Alternatively you could use a different program to burn the CD, such as (free) CDBurnerXP