AutoCAD is a powerful computer-aided design (CAD) software that allows users to create detailed 2D and 3D models of a wide range of objects and structures. If you want to learn how to build a 3D model in AutoCAD, follow these steps:

1. Start a new project: Open AutoCAD and create a new project by going to “File” > “New.” Select the appropriate template for your project and click “Create.”
2. Set up your workspace: Go to “View” > “Viewports” and choose the “Four: Left” option to set up a four-viewport workspace. This will allow you to see your 3D model from multiple perspectives as you work.
3. Create basic shapes: Use the “3D Modeling” tools in the “Home” tab to create basic shapes that will form the foundation of your model. You can use the “Box,” “Cylinder,” and “Sphere” tools to create these shapes.
4. Modify shapes: Use the “Modify” tools in the “Home” tab to modify the shapes you have created. You can use tools like “Move,” “Scale,” and “Rotate” to change the position, size, and orientation of your shapes.
5. Add details: Use the “3D Modeling” tools in the “Home” tab to add details to your model. You can use tools like “Extrude,” “Revolve,” and “Sweep” to create more complex shapes and features.
6. Render and save: When your model is complete, go to the “Render” tab and use the “Render” tool to create a final image of your model. Save your model by going to “File” > “Save As” and choosing the appropriate file format.

By following these steps, you can create a detailed and accurate 3D model in AutoCAD. As you become more familiar with the software, you can explore more advanced techniques and features to further refine your models.