Switch the Workspace from Drafting & Animation to 3D Modeling (top of screen).

From the Mesh tab, under Mesh Box, select the box primitive and adjust the divisions.

Select the Mesh Box and draw a cube of a suitable size (a multiple of 5 would be neater).

In the Selection area - change No Filter to Vertex and move the corner points.

In the Convert Mesh section - Convert to Solid and change the view to shaded or realistic.

Three adjacent vertices can also be moved to the points to sharpen the solid form.

Further editing can be performed by converting to NURBS and showing CV (control vertices) under the Surface tab.