The Extrude tool 
in Blender is a simple, often-used tool that extends the geometry length by adding extra geometry instead of changing the size. Extrude works in Edit mode with Faces, Edges and Vertices, but it works slightly differently for each. The extrude tool also has a nasty side effect if you are not careful, but more about that later.
Extruding Faces
Lets look at our trusty cube. Select the cube and switch to Edit mode 
. Change to Face Select mode 
, and click a face:
Now, while the face is selected, type and move the mouse (don’t click yet).
Move the mouse to the right again and left-click 
:
By modifying the value in the Z field, you can set the extrusion distance precisely. Change it to 3m, press 
and the parametric Pop-up panel disappears. (If you want the panel back press 
).
Now switch to object mode , move the cube to the right 
and add a new cube 
:
Toggle back to Edit mode , select the face and move the face 3m forward 
to give it a total length of 5m:
The two objects are the same size and shape but the right-hand rectangular object had 10 faces while the left-hand object has only 6. We use Extrude and not Move because we want the extra face geometry for later operations.
Sometimes, Move and Extrude have different effects. If we select the top 3m x 2m face and Move it vertically up by 2m 
, the other faces expand and stretch to accommodate the move:
If, on the other hand we select the same top 3m x 2m face and Extrude it vertically up by 2m , new faces are generated to accommodate the extrude:
Warning
The extrude tool has a nasty side effect unless you are very careful. When you type , click a face and then change your mind and press 
to cancel, you wind up with a second face directly on top of the selected one. Don’t believe me?:
Why so many more edges and faces if only 4 extra vertices have been added? Think about it this way – if there was a completed extrude process, the extra 4 Faces and 8 edges would be produced. But when cancelled, the faces are still produced, they are just on top of each other. To fix this, you need to merge vertices. See here how to do it.
Extruding Edges
While most extrusions are face extrusions, occasionally, we extrude an edge. The same extrusion principles apply – the edge gets duplicated and moved, and a face is created joining the original edge and the new edge:
The same warning applies – If you cancel an extrude, perform a merge vertices operation.
Extruding Vertices
In the process of creating a unique shape, we often extrude vertices to create a set of edges. Let’s say we wanted to trace a shape and then give it some volume. Switch to edit mode . Activate Vertex Select mode 
.
Change from Perspective to a ortho viewport 
.
Add a single vert by typing and the choose Add Single Vert:
Select the Vert and extrude it by typing . Move the mouse and left-click .
Type again, move the mouse and left-click .
Type again, move the mouse and left-click … and so on until you get to the last vertex position:
Select the first vertex and the last vertex and type 
. The two vertices are joined with the fill tool.
Now Box-Select all the vertices in the shape, press again and an Ngon is created filling the shape:
Finally press and drag 
the middle mouse button to get out of Ortho View, and with all the vertices still selected, extrude the Ngon upward to get a 3D shape:
And don’t forget, if you cancel an extrude, perform a merge vertices operation.
