Where do you start? Music learning is similar to language. Its starts with listening (exposure) by playing music at home, playing an instrument or singing songs. A musical home environment is really the best way to inspire and introduce your child to learning music.
What songs should you play or sing? Remember its like learning a language so although most music will be good they recommend more relaxing music. Babies can be sensitive to loud sudden noise as we all are if we were not expecting it I guess.
I found a great website full of children's songs called BusSongs.com As far as I can tell its free and will give you access to lots of children's song and includes the lyrics, melody and even some videos.