Songs not showing up on the iPod, but on finder yes

i reccently found a 4g ipod and i reseted it and all stuff with finder . then im trying to put like a song in y ipod but it doesnt work! i mean it copies in ipod but not showing up . then i tried to like reset it like with like the middle button and the menu butto but still not showing up? the song is mp3 and tried installing it in a higher and lower version but still not showing up , and i eject the ipod correctly so that shouldnt be a problem . the music worked before on the ipod but i just wanted all deleted. and im not sure it the ipod needs to connect to the wifi or something or if i should put the songs in itunes?! i need help asap