Though at this point his vocabulary likely consists of only a couple of words besides "mama" and "dada," your baby can probably babble short, fully inflected sentences that sound like he's speaking a foreign language. Act as though you understand.
Your baby may be able to respond to simple questions and commands, especially if you give him some clues with hand gestures. For example, ask "Where's your mouth?" and point to it. Or try "Hand me the cup" and point to the object. He may even answer you in his own way, using his own gestures, such as shaking his head for "no."
Because he's receptive now, it's a good time to begin to teach your baby how to help out. Emphasize "please" and "thank you," and make toy cleanup time fun by turning it into a game. Though he probably won't get the idea just yet, it's not too early to start. Break the task into very small parts. At this age, he'll need you to work with him by his side.
It's up to you to help your baby make connections between objects and their names the more you do, the faster your child's vocabulary will grow.
Keep talking to your baby and labeling things. Count stair steps as you climb them, and point out the names and colors of the fruits and vegetables at the grocery store. Read your baby a picture book and ask him to point to or name familiar objects.
Solicit his opinion once in a while: Ask him if he'd like to wear the red or the blue socks, or if he'd like to play with his blocks or his stacking rings. Give him only two choices both of which are right in front of him. He may not answer, but then again, he may surprise you.