First, pls make sure you use the latest iTunes version for your iPod Touch. Just open iTunes and connect your iPod to the compute. Once iTunes recognize your iPod Touch you may click Music in the navigation bar and select the music you want to transfer. Click the songs you ve chosen and drag them onto the iPod menu in the navigation bar. Wait for a few minutes and you can see them on your ipod. Done!
If you dont wanna use itunes or wanna find another easy way, then just google iPod Transfer
to seek some useful tools