Extruding entities is one way to create 3d solids. With extrude you can select linear entities but with 'Extrude Stories' you can select hatches. The command works best when the hatches are created with closed polylines. For every hatch the command will look on which layer it's drawn. 'Extrude Stories' uses the information you put at the end of the layer name. If a layer is called 'layer-4' for example the command will use 4 as value. This is not the value used as extrusion, it will be treated as a number of stories or levels. The extrusion the command will make is based on a plinth value and a story value you define. The plinth value is the base level and the story values are all levels on top of that. If the values for the plinth is for example 4.0 and the value for stories 3.0 and the number at the end of your layer is 4, the command will make an extrusion of 13.0. It will take 4.0 for the base. That means that there are three stories left, 3 x 3.0 is 9.0. So the complete extrusion is 13.0. To emphasise the stories, you can show the division. In that case the command will create an individual extrusion for each level.