The OptiX Programming Guide must always be your first reference when trying to learn OptiX, but there are many additional resources.
NVIDIA raytracing documentation hub: https://raytracing-docs.nvidia.com/
Please always refer to the online documentation which are more up-to-date than the documents shipping with the SDK releases.
For the old OptiX API, there is my OptiX Introduction GTC presentation video at the bottom of this page: https://developer.nvidia.com/rtx/ray-tracing/optix
Slides are here: https://on-demand.gputechconf.com/gtc/2018/presentation/s8518-an-introduction-to-optix.pdf
(This will also be found via the GTC on-demand link further down.)
The example source code can be found here: https://github.com/nvpro-samples/optix_advanced_samples
Related sticky post on this forum: https://forums.developer.nvidia.com/t/optix-advanced-samples-on-github/48410
Note that this was using OptiX 5.1 at that time, so it’s not touching on the built-in triangle primitives which were added in OptiX 6.0 to be able to make use of the hardware accelerated triangle-intersection on RTX boards.
I made the examples compile with OptiX 6.5.0 as well, but depending on the MSVS used, you might need to set the CUDA_HOST_COMPILER location manually. MSVS 2017 and newer changed the compiler location.
https://github.com/nvpro-samples/optix_advanced_samples/issues/17
Look at the other issues in that repository first if you have issues building the examples.
While the first four introduction examples there are pretty basic, the later ones implement a full global illumination path tracer with a very flexible renderer architecture which is not showing the maximum possible performance in favor of elegant code.
I ported some of the later introduction samples to OptiX 7 here: https://github.com/NVIDIA/OptiX_Apps and added some even more advanced examples showing multi-GPU distribution and resource sharing via NVLINK. (Also explained inside the sticky post link above.)
I did not port the simpler examples because there is also an OptiX 7 SIGGRAPH Course which showed the more basic steps, similar to what some of the OptiX SDK samples show. https://github.com/ingowald/optix7course
All linked in this post as well: https://forums.developer.nvidia.com/t/optix-7-2-release/156619
There are also a lot of other interesting OptiX GTC presentations, esp. the ones from David about the new features in each OptiX 7 release, but there are also older ones including my OptiX introduction from 2018.
Just search for OptiX here: https://www.nvidia.com/en-us/on-demand/
If you have any question about OptiX, please check the resp. Programming Guide and API References first, then search this OptiX forum for related topics. Many things are already answered here.