Blender doesn't say "start with a cube". Its default "General" scene has a cube. You can add whatever mesh, text, curves, metaballs, grease pencil, volumes, etc you want.

As far as workflows go, there are far too many to list, and most artists use multiple, but common ones are:

* Sculpt from a base mesh, increasing resolution as you go with remeshing, subdivision, dyntopo, etc. * Constructively model with primitives and boolean modifiers. * Constructively model with metaballs. * Do everything via extrusion and joining, as well as other basic face and edge-oriented operators. * Use geometry nodes and/or shaders to programmatically end up with the result you want.