Widgetizing the content area?

While working on a project recently [using GeoPlaces theme], I came to know that the widgets can be placed in the content area section as well – which I initially thought is not possible.
I did try to find any book article which explains how can we enable a Widget to output in the main content area of a blog. To my surprise I could not find any? I will appreciate if anyone can point me towards one? or explains a little bit of it by providing some code example.
TIA