The Guide -> The Concepts -> Vertex Editing

To enter vertex editing mode, click the vertex editing button is the modes section of the left hand toolbox.

You can also bind a key to switch vertex editing on and off. Bind a key to the following command:
MODE SHOWVERTICES -1

1. Set the vertex color to something bright (like white)
   Goto View->Advanced Options->Editor->Color->C_BrushVertex and change it to white
   This will mean that the vertexes should now show up properly
   N.B. Post version 430 this should be set up automatically.
2. You can screw up your complete map if you get this wrong, so always do a save!
3. Don't forget you can create 'invalid' surfaces if your not careful, e.g. a square surface with one vertex below all the others is not valid
4. I've had lots of trouble with single vertex editing and always use the drag-select detailed below
5. I've come across various glitches on my PC check out my "Vertex Bugs" at the bottom!

The first thing you must do is select the brush you want to edit. Simple clicking on the brush should accomplish this task.

Clicking on the vertex should select each vertex. (It doesn't work on my PC, but hey, thats life)

Holding down control and clicking should select more than one vertex.

The function is used by holding down the Ctrl+Alt keys, then left clicking and dragging a box around one or more vertexes. It is best if you release the mouse button before releasing the keys, as sometimes it might leave the box on screen if you do it the other way around.

If you want to select vertexes from more than one brush then hold down the Ctrl key and select the brushes in the normal way, you will see their vertexes appear as you do. Then you can select their vertexes in the the above manner or using the Drag-Select manner described here.

The vertexes which are selected are defined by those which are contained within the drag-box.

You move vertexes exactly like you move brushes, holding down the Ctrl key and Left-Mouse button and moving the mouse. I find it is best to press the Ctrl key first, then the mouse button. After moving depress the mouse button before releasing the Ctrl key.

If you select some vertexes and then click in another view it may deselect your vertexes. If you hold down the Ctrl key as you click on the next view this should keep them selected.

Aside from the above mentioned fact that I cannot get single selection of vertexes to work I have to say that vertex editing finally seems to have settled down.

One reason for this is I believe the fact that you can no longer move and entire brush while in vertex editing mode (aside from selecting all the vertexes obviously!)