Creating an edge between two vertexes I'm trying to model a bar front, but I'm having problems extruding the right part of the face.

I keep trying to add a vertex between two points of a sized up cube object but it isn't allowing me to connect the two, giving me the error invalid selection.

Any ideas on how I can do it please?

Its the triangle shape I'm trying to get 



Bar front I'm trying to model
Make smart use of modifiers here. You have a repeating shape, use an Array modifier instead of modelling it all one by one by hand.

For the face keep it simple. Just use the Poke Faces Alt + P operator on a simple unsubdivided face.

Move the resulting vertex down to vertically align with the bottom vertex of the face, then move it forward to make the protruding "pyramid" shape.