i cant tranfer my ipod music to my computer without loosing a lot of it help

i bought a new computer and i have itunes but i seem to have lost music i originally put on it

i didnt buy all of it from apple some was from cd,s i dont have any more i do have all of the music on my ipod and want to add it to the computer i tunes library and cant without loosing it .

how do i tranfer music from ipod to library manually ? thanks