Once selected, click this button to extrude in any of the editor's views, but the best control is done in one of its 2D views. Each time a new drag is made a new set of faces, or vertexes, will be created from that starting position to the position at the end of the drag with the new faces, or vertexes, selected. Switching from view to view between drags will change the extruded drag direction.

Face mode : Extrude Selected Faces This function only works with selected faces in the Editor's views and the Linear Drag Handles button is active.
No bulkheads will be created.

Vertex mode : Extrude outside edges This function only works with selected vertexes in the Editor's views and the Linear Drag Handles button is not active.
It will perform the same function for all 'outside' edges (do not share two common vertexes) that have been selected. Two vertexes of the same triangle must be selected. If an improper vertex selection has been made it will attempt to correct that selection or notify you if it can not.

Once selected, click this button to extrude in any of the editor's views, but the best control is done in one of its 2D views. Each time a new drag is made a new set of faces, or vertexes, will be created from that starting position to the position at the end of the drag with the new faces, or vertexes, selected. Switching from view to view between drags will change the extruded drag direction.

Face mode : Extrude with bulkheads This does the same function as the 'Extrude' but leaves bulkheads between each extrusion drag. This function only works with selected faces in the Editor's views and the Linear Drag Handles button is active.

Vertex mode : Extrude all edges This function only works with selected vertexes in the Editor's views and the Linear Drag Handles button is not active.
It will perform the same function for all edges that have been selected, including ones that share two common vertexes.At least two vertexes of the same triangle must be selected. If an improper vertex selection has been made it will attempt to correct that selection or notify you if it can not.

If faces of a model component have been selected, the direction they face will be reversed by clicking this button.

If faces of a model component have been selected, those faces will be split, at the middle of the longest edge, into 2 new triangles when this button is clicked.

If faces of a model component have been selected, those faces will be split, from the center to all 3 points of each selected face, into 3 new triangles when this button is clicked.

If faces of a model component have been selected, those faces will be split, at one point and the middle of all 3 edges of each selected face, into 4 new triangles when this button is clicked.

Face Cut tool:  (first button of the two)
When this button is active, at least one frame and faces of a model component have been selected, a LMB drag can be made to produce a red cut line, like in the map editor, across them. Where the line crosses it will divide each face into 3 individual triangles.

To cancel the cutting, press the RMB & LMB together then let go. This can be done at any time.

Different cut patterns can be achieved sometimes, depending on the selected faces mesh structure. To test it out click on the Reverse face direction button two times, once to reverse them and once again to reverse them back to the direction they were facing before. This can rearrange their individual vertex order thus causing the change in the cut pattern. If you do not like the results just use the Undo / Redo function to the point before the faces where flipped.

Keep Dupe Vertexes:  (second button of the two)
This option ONLY works with and applies to the 'Face Cut tool'. The default setting is inactive, causing all duplicate vertexes to be combined when a face is 'CUT' so that the new faces do NOT pull apart. When ACTIVE (on) all common vertexes of the new cut faces CAN be pulled apart for further editing (to extrude, leave open, add new faces to and so on). At any time they can be 'WELDED' together using the Merge Vertexes function.