The rendering process, especially for big scenes and complex effects, reminds a bit of film photography:
You build the scene, you place the lights, the materials, you set the shot you want, you launch the rendering process, and then you wait to see the results.
Seconds, minutes, hours, days... depends on the scenic complexity, the selected settings, the resolution, the light refractions and the plotting of the shadows.
It is a work of intuition, in which you cannot have an immediate visual response.
While getting better, You will avoid vasting too much time with errors.
Luckily, is possible to separate the scene in "Render steps": one, perhaps for the contours of the objects, one for the shadows, one for the objects themselves, one for the reflections (etc etc).
The images can then be assembled into "compositing" software.
