How create cube

U have face made from four vertexes. Is possible in really simple way made from it cube.

Select all four vertexes – now is selected face too.

U can see blue „normals“. They are showing in what direction is face… erm… facing J

Now lock X axis in „left „ view.

There is control window for „extrude“ function.

Set number in it at 1 – it controls in how much levels will be face extruded.

Now press „G“ – it will activate „extrude“ function.

Hold right mouse button and drag to this side in what are normals showing

Now u have object looking like this one:

So u need close this open side. Select vertexes at opened side…

…and press „F6“ again. Hole is closed. Now u got cube.