In the Projects tab of Unity Hub, click on the blue New project button.

Select the 3D Core project template. Then, rename your project and select the project's storage location. Click the blue Create project button to finish.

Click on your project to open it.

Unity has support for a few different 3D file formats, including .OBJ and .DXF files.

Right-click in the Assets window and click Import New Asset...

A file directory window will open. Navigate to your 3D file and click Import. Your 3D file will appear in the Assets window.

Drag and drop the 3D file from the Assets window into the Hierarchy window. You'll see your 3D object appear in the Scene window.

You can change the object's position, rotation and size with the Transform controls in its Inspector window.

Select the Main Camera in the Hierarchy window and adjust its view using the movement and rotation tools to center the Scene. This affects your view while in gameplay mode.

Right-click in the Assets window. Select Create and Material to create a new color mask.

Click in the Albedo window to change the color of the Material. Other attributes of the Material can be edited here as well.

Drag the Material from the Assets window to the object in the Hierarchy window. The object will change appearance and you can edit the Material settings in the object's Inspector window.