Batching draw calls?

While reading the Rendering Statistics Window article over here: http://unity3d.com/support/documentation/Manual/RenderingStatistics.html

I saw that "Batching draw calls" is pretty useful, but there is no further explanation about how exactly I achieve such thing. Can someone help?

Number of draw calls that where batched together. Batching means that engine will be able to combine rendering of multiple objects into one draw-call which leads to lower CPU overhead. To ensure good batching you should share as many materials between different objects as possible.

How do I "share materials" between objects?