Teaching Baby Sign Language?

That other person was right about you being able to understand your baby. It's a mom thing.

But it's cool you want to teach your baby to know other languages, and at a young age is when they'll learn the most quickly.

Books are tough to use because it only gives a 2-dimensional static picture. What you should do is find someone that knows sign language and have them teach you basic signs for things like hungry, more, finished, etc. Then when you talk to your baby, use the signs as you use the words. When you ask, "Are you hungry?" give the sign for hungry. The baby will pick up very quickly.