OpticStudio [9] Non sequential ray tracing_OpticStudio non sequential mode (1)
This page describes OpticStudio's "non-sequential ray tracing" along with the differences from the sequential ray tracing.
Non sequential mode
OpticStudio 
OpticStudio [6] ZDA file and analysis functions_OpticStudio sequential mode (5 fin)
This page explains the questions that you always have when you start using OpticStudio, "What is ZDA files?" and "Points to be aware of with the analysis function".
OpticStudio [5] Two coordinate systems_OpticStudio sequential mode (4)
This page describes "local and global coordinates" and "right handed coordinate system", which is essential knowledge of OpticStudio.