How to connect 2 vertices with edges? This sounds as a very basic question, I guess I just don't know proper terms to find the answer at once..

I'd like to create a complex polyhedron, so I'd like to create a tetrahedron first. Starting from a cube, I can get a figure like the one below (by deleting some faces and edges), but how do I connect those vertices with 3 missing edges?

Although the main question is the one in the title, other advices about creating a tetrahedron are welcome, too.
The answer is simple. Just press F between two vertices.

And your tetrahedron problem can be solved as follows:


Start with a Plane.
Delete one vertex and join all vertices with F to make a triangle.
Subdivide the triangle.
Go to the outer vertices and scale them on the xy axis to 0.
In the last step you only have to move the selected vertices on the Z axis by one.




That's it.

(Of course, don't forget to swap normals.)