All extrudes from faces occur in a perpendicular direction from the
selected face (Figure 3.7).
Figure 3.7 - Extrude with a size of two
In case you want to extrude from an edge or vertex, you might want to
constrain the transformation to an axis.
3.2.1 Extrude modes
Besides the E key, you can also trigger the extrude using the options
from the Toolbar. There you will find four buttons with different types of
extrudes (Figure 3.8).