Everybody has heard or used baby talk in their life. Babies come up with creative ways to say words they can't otherwise pronounce for lack of understanding, lack of teeth and just general lack of knowledge of the English language. When babies begin to get attached to items, they tend to name them close to what they actually are but in most cases they won't be able to verbalize them how we're used to saying them. You get words like botties for bottles, binkies for pacifiers and bankies for blankets. This is later in life, though, when a baby first begins to "speak," it's more a production of sound as opposed to actual words. If you're lucky a child might pick up a word or two before their time, but most development in a healthy environment takes place slowly.
However, when it comes to the first sounds your child will make, generally this will be confined to syllables strung together in such a way to kind of sound like something but to be more nonsense than anything. Such syllabic strings as "mama" and "dada" are familiar, because they refer to mommy and daddy. Most children end up saying mama and dada long before they can ever say mommy and daddy; no matter how much you tell them it's mommy and daddy, they will not be able to pick it up simply from you saying it. Until they develop further, physically, not mentally, they won't be able to use their mouth, tongue and jaw to actually pronounce words. You can try all you want, but they won't be saying antidisestablishmentarianism anytime soon no matter how many times you say it to them.
This doesn't mean you should give up trying to encourage your child to speak, you just have to learn to adapt to the language they speak until they can better enunciate words and put together sentences. This takes up to five or six years in some cases, but by then, your child will have learned how to use their physical capacities to pronounce words you wish they would've said years ago. Don't despair! It's all apart of your baby's learning experience and in time they will be able to speak with the best of speakers.