I HAVE A SONY N50 DIGITAL PLAYER...WHAT SHOULD I DO FIRST TO LOAD SONGS TO THE PLAYER

Sony Network Walkman does not support adding / removing of files, or formatting if it is not done from SonicStage, their software.
If music is added of removed from windows explorer or other software, the player gives an error message 'No data' or something similar.
To fix the problem, download and install SonicStage from Sony support website.
Select your model and click continue, then scroll down, select your operating system in the select box to the bottom of the page and select the software you want to download...
After installing, connect the player to your computer and select 'format' from the menu (This will remove all data from the player, so you might want to make a backup).
Now transfer your music files to the player using sonicstage.

Good Luck