What is the best way to teach a baby of 1and a half years to talk

The tried and true method is talking to than in a normal voice with real words... not baby talk, read them books. Kids learn this by watching and listening... its hard wired into their brains.

Children have learned to talk without overanalyzing the process for hundreds of thousands of years. And did it quite well too. And mothers without ANY education at all managed to do it this way.

Assuming you are not talking about a special needs child.

Just to add... don't worry if your child does not have a large verbal vocabulary just yet. At this stage they will have a far greater understanding of words and meaning than what they will actually be able to speak.

And don't always get things for them if they just point or grunt at things.