Q:

Is there a Solidify Extrude function?

The normal Extrude works like this: take selected geometry and move to another place. But I need something that leaves the selected geometry where it is and duplicates it.
I noticed that when you extrude a simple plane it generates a cube. How do I achieve that but just with a larger pool of polygons?

A:

Try ⎈ CtrlF> Solidify:

Note that in many cases (including the example in the gif), this will probably result in non-manifold geometry.

