How do I delete a face? By hollow, I mean that I want only the sides and the base of the frustum to be visible. I already have a 3D Cone Frustum so now I only want to subtract the inner regions from the cone. So, my question is of course, how to do that ? I thought of using boolean but it only shows the option of a cone, so is it possible to use another one as a boolean modifier ? if yes, then how. I am a total noob and hence forgive me if its a bad question.Thanks in advance.
In Edit Mode enable Face select right click on the top face you want to remove.



Then press X or Delete. This shows the Delete popup menu, where you can select Faces.