<li>the type of elements which will be extruded (1D or 2D),</li>
<li>specify the IDs of the elements which will be extruded by
selecting them in the 3D viewer or select the whole mesh or
-submesh,</li>
+submesh,
+<ul>
+<li>Check on <b>Select the whole mesh, submesh or group</b> option
+<li>Choosing them manually with the mouse in the 3D Viewer. You can
+click on an element in the 3D viewer and it will be highlighted</li>
+<li>Applying Filters. The <b>Set filter</b> button allows to apply a
+definite filter to selection of the elements. See more
+about filters on the
+\ref selection_filter_library_page "Selection filter library" page.</li>
+</ul>
+</li>
<li>specify the distance at which the elements will be extruded,</li>
<li>specify the vector along which the elements will be extruded,</li>
<li>number of steps.</li>
