# Concepts

* [What is Debugging?](https://www.xrdev.app/mixed-reality-docs/lessons/lesson-2/concepts/what-is-debugging)
* [What makes a 3D model? What are Polygons, Splines, Vertices, Meshes and Materials?](https://www.xrdev.app/mixed-reality-docs/lessons/lesson-2/concepts/what-makes-a-3d-model-what-are-polygons-splines-vertices-meshes-and-materials)
* [How to choose performant 3D models?](https://www.xrdev.app/mixed-reality-docs/lessons/lesson-2/concepts/how-to-choose-models-for-your-app-for-performance)