This is quite and easi task
with a blank screen, click on the "Vertex" tool and goto one of the veiws. Mark out a triangle pointing down with 3 Points ... now click on the "Face" tool.
Click on the Top Left Vertex (which by defualt would be a white/red dot - depending if its selected or not)
next click on the bottom vertex, notice there is a line there - this means the connection has started ... click on the Top Right one and there you have it a complete Forward Facing Polgyon/Triangle Face
Now make another triangle of Vertex to the side of the first one however click on them the opposite way.
And that is a Back Faceing Polygon.
They're called that becuase one faces towards the camera your working on and the other faces away, or rather has its back to the camera
The backs of polygon aren't rendered within games, so it is good to know why you're objects appear to have holes.
If you noticed, a Forward Face is an Anti-Clockwise connection whereas a Back Face is a Clockwise connection. I've personally found it easier to remember it that way
now to select and edit them click on the "Select" tool and you'll see the menu below will change - now click on "Vertex" ... you'd select Vertex just as you've drag a box to select an area in Paint. As your in Vertex mode you're only editing on this level, so only the Vertex will appear Red to denote you've selected them. If you find there are vertex you still want to select, rather than simply trying a new selection box - press Shift (only whilst in Select mode other wise it Zooms the veiw
) and select the extra Vertex
you can click anywhere to deselect.
to move simply click on the "Move" button, and it'll move whatever you have selected at the time
One last thing, you cannot edit within the 3D veiw - so please don't say "why can't i select my vertex or faces in 3D?" because you can't do anything there, its just to preview the model.
hope that helps
Anata aru kowagaru no watashi!