There are a number of ways to create a 3D model or an entire scene. Some sculpting applications allow you to create and shape polygons, ultimately forming a 3D asset. This type of modelling might, for instance, be particularly suited to creating organic assets — such as plants or people — as it is well suited to an artistic interpretation of somewhat irregular shapes.
Alternatives to this approach exist. Other modelling tools focus on creating edges and surfaces, rather than polygons, in a three-dimensional space. Creating 3D assets in this way allows for great mathematical precision and such tools are often used in industrial design or computer-aided design (CAD) modelling.
Or you might opt to “scan” an existing real-life object using a specialised tool — the data captured from such a scan will allow you to re-create the object in a 3D space. Or you might prefer to go the route of procedural generation, in which your software sculpts a model for you based on a set of previously established mathematical rules.
However you create your 3D model, the next step is texturing.