This is just a brief summary, but it explains how we start with an AStaticMeshActor containing a cube, change to the render proxy and combine it with render data, and then send the commands to the RHI command list. Finally, the GPU executes them in many passes and gives us the final image.
While there are many more details to consider, such as instance culling, primitive data transfer, and GPU Scene, let's use this image as a starting point. We'll discuss the specifics, and I'll indicate where each detail fits within the context of the image.