An introduction to computer audio
You have your music on your PC but you also want it on a portable.
Often people do so by maintaining two libraries say one in lossless e.g. FLAC and a copy in MP3 for the portable.
You better look for a media player supporting transcoding.
Transcoding is converting on the fly to a format supported by the portable.
Transcoding relieves you of the burden to maintain duplicate libraries.
Your audio collection probably won’t fit on your portable.
The trick is to make a play list and use this for the synchronization.
Well-designed media players allow you to do so.