What do RenderForwardOpaque::Sort/Render/Prepare do?

In my profiler I see that the majority of the time spent in the CPU Thread is spent in RenderForwardOpaque::Sort, RenderForwardOpaque::Render & RenderForwardOpaque::Prepare.

And when I say within these methods, I mean the 'self ms' shows that most of the execution time is within these methods themselves, not any subsequent calls.

What do these methods do? Or, how do I find out what they do, so that I can optimise my scene to reduce the amount of work they have to perform?