To create an Hexahedron in the Main Menu select Model -> Construction -> Add Hexahedron.
There are two methods to create an Hexahedron.
The Hexahedron can be defined its faces (quadrangles).
Arguments: Select from 2 to 6 quadrangles.
The dialogue box to create an hexahedron from quadrangles is:
Create an Hexahedron from quadrangles
The Hexahedron can also be defined by its vertices Vertex 1, Vertex 2, ..., Vertex 8.
Arguments: Select 8 vertices.
The dialogue box to create an hexahedron from vertices is:
Create an Hexahedron from vertices
TUI command: Hexahedron
About hexahedron: Appendix: naming rule to find elements in an hexahedron