It's kind of a funny question. How do you teach your baby how to speak? Babies learn from us by copying us, so the best thing is to teach your baby to speak how you want your baby to speak.
I don't believe in speaking to a baby in baby talk, because you don't want your baby growing up speaking baby talk. Of course, you can be affectionate and cuddle your baby, but you should speak to your baby just like you would speak to your friends or another child. Babies will mimic anything that we do if we do it slowly and properly.
So, if you want to teach your baby certain words, when you hold the bottle say bottle. But if you're going to hold the bottle and say bah bah, you're baby's always going to say bah bah. Your baby will never learn that it's called a bottle, because you've always called it a bah bah. If you want your baby to call you momma, say momma. If you want your baby to call you dada, say dada. But don't expect a baby to learn a new word if it wasn't spoken to them.
I often find medical students who come and round with me in the hospital speak baby talk to all the babies because they think that the babies will like them more if they speak baby talk. Babies will like you if you're affectionate and if you're warm. You don't have to speak baby talk to get your baby to speak.
Babies should start making sounds at four months of age. At six months of age they should make more consonant and more vowel sounds. Babies often have their first word, like hi or dada, at nine months of age. But some babies don't have their first word until one year, and that's fine.
Babies who hear two or three languages at home may have some speech delay, and this is OK. Make sure you bring it to your pediatrician's attention, because we want to make sure that those babies can hear well if you think that they have speech delay, and that too many languages are not confusing them. We have some patients whose parents each speak a different language, then they have a babysitter that speaks a third language. For these babies it's often confusing, which language do I choose to speak.
I'm not saying not to introduce foreign languages. Foreign languages are wonderful for babies, and babies learn languages better when they hear them younger. Just know that it might involve some speech delay.