How do I transfer all my songs from my iPod to my iPad?

You don't. If the songs where purchased from iTunes you can download them from the iTunes Store App Purchased section assuming you are using the same Apple ID on then iPad that bought those songs.

Otherwise, you will need to sync the songs to the iPad the same way you did to the iPod. From a computer running iTunes that has your song library.

Copy to iTunes and then sync to the other device

Recovering your iTunes library from your iPod or iOS device: Apple Support Communities