There are a many different ways to extrude geometry in Zbrush.
If modeling at low poly, ZModeler has several extrusion options : QMesh, Extrude, and Transpose.
Transpose mode (either via Gizmo or the transpose action lines) can both extrude geometry. The direction the geometry extrudes depends on how you have the manipulator oriented, so it’s a good idea to understand the controls of these modes.
In addition, geometry can be extruded in the Tool > Geometry> Edge Loop menu.