Extrude, please explain how it works

[SolidsnakeIT]

Hi, I'm trying to use Goxel on desktop platform and on iOS. I like it :)

Question about extrusion: can you explain how it works?

Sometimes I can do it, other times it doesn't work and I feel stupid.

In particular I thought I had to select an area and manage the extrusion of that area but it seems not working.

Thanks for your help