The best way to start understanding how 3D software works is to gain an understanding of 3D computer graphics principles. This means learning the basics of 3D math, such as vectors, matrices and quaternions, and how they are used to represent and manipulate 3D objects. You'll also need to understand how basic 3D rendering works, such as how lights and materials interact with objects to create an image. Finally, you'll need to understand how 3D software packages are structured and how they interact with the hardware they run on.
Once you understand the principles that make 3D software work, you can then start to look at specific software packages and get a better understanding of how they work. Most 3D software packages have comprehensive tutorials and user manuals available, so it's worth taking the time to read through these and understand the features and tools that are available.
Finally, it's always a good idea to experiment with the software and see how it works in practice. This will help you get a better understanding of the limits and possibilities of the software, and will also give you a chance to practice the skills you have learned.