[ Music & Music Players ] Open Question : how to upload music from itunes to my ipod touch?

ok so i just got this ipod touch for my birthday and i don't know how to add music to it i already have music in my library cause i had an ipod before it but every time i hook up my ipod touch and i go to file and down to sync ipod it won't let me click it so how do i upload the music ?? please help me thanks