There is no definite answer to this as all children progress differently. First words will generally start in the first 2 years as simple ones such as "mommy," "daddy," "baba" etc. According to babycenter.com:
In utero Many researchers believe the work of understanding language begins while a baby is still in utero. Just as your unborn baby gets used to the steady beat of your heart, he tunes into the sound of your voice. Days after birth, he's able to discern your voice among others.
Birth to 3 months Crying is your baby's first form of communication. And one cry doesn't fit all: A piercing scream may mean he's hungry, while a whimpering, staccato cry may signal that he needs a diaper change. As he gets older, he'll develop a delightful repertoire of gurgles, sighs, and coos.
As for his ability to understand language, he's starting to pick up what words sound like and how sentences are structured as he listens to those around him. Linguists say babies as young as 4 weeks can distinguish between similar syllables, such as "ma" and "na."
4 to 6 months At this stage, your child will start to babble, combining consonants and vowels (such as "baba" or "yaya"). The first "mama" or "dada" may slip out now and then. Though it's sure to melt your heart, your baby doesn't equate those words with you quite yet. That comes later, when he's almost a year old.
Your baby's attempts at talking will sound like stream-of-consciousness monologues in another language, with endless words strung together. Vocalization is a game to your baby, who's experimenting with using his tongue, teeth, palate, and vocal chords to make all sorts of funny noises. At this stage, babbling sounds the same, whether you speak English, French, or Japanese in your home. You may notice your child favoring certain sounds ("ka" or "da," for example), repeating them over and over because he likes the way they sound and how his mouth feels when he says them.
7 to 12 months When he babbles and vocalizes now, your baby will sound as if he's making sense. That's because he's trying out tones and patterns similar to the ones you use. Foster his babbling by talking to him and reading to him.
13 to 18 months Now your child is using one or more words, and he knows what they mean. He'll even practice inflection, raising his tone when asking a question, saying "Up-py?" when he wants to be carried, for example. He's realizing the importance of language as he taps into the power of communicating his needs.
19 to 24 months Though he probably says about 50 to 70 words now, your child may understand as many as 200 words, many of which are nouns. Between 18 and 20 months, he'll learn words at the rate of 10 or more a day (so watch your language!). He'll even string two words together, making basic sentences such as "Carry me."
By the time he's 2, your child will use three-word sentences and sing simple tunes. His sense of self will mature, and he'll start talking about what he likes and doesn't like, what he thinks and feels. Pronouns may confuse him, which is why he might say "Baby throw" instead of "I throw."
25 to 36 months Your toddler may struggle for a while to find the appropriate volume to use when talking, but he'll learn soon enough. He's also starting to get the hang of pronouns, such as "I," "me," and "you." Between ages 2 and 3, your child's vocabulary will grow to up to 300 words. He'll string nouns and verbs together to form complete, simple sentences, such as "I go now."
By the time he turns 3, your child will be a pretty sophisticated talker. He'll be able to carry on a sustained conversation and adjust his tone, speech patterns, and vocabulary to his conversation partner. For instance, he'll use simpler words with a peer, but be more verbal with you. By now he may be almost completely intelligible. He'll even be a pro at saying his name and age, and will proudly oblige when asked.