Those random chatters are on the rise as your baby's ability to vocalize improves. Like a singer doing warm-up exercises — or a scientist puttering in a lab — your baby is trying to use parts of her mouth and vocal cords in different ways to make sounds. You may begin to hear two-vowel combination sounds like "ma ma" (which still doesn't refer to you directly but is rewarding to hear, anyway!). Encourage your baby's experimentation by talking directly to her with lots of expressiveness and facial emotion.
Even though you can't understand your baby, she is beginning to be able to understand you. That's why it's important to talk to her as you move through the day. Narrate what you're doing: "Here's your bottle." "Ready for your bath?" In a few months she will understand you perfectly when you say the word "bottle" or "bath." You don't have to be a nonstop chatterbox; babies appreciate quiet, too. All you need to do is converse with her like the little companion she is. (Even if the chat is pretty much one-sided.)

From babycenter.com