Welcome to the forum!
That's a very open-ended question, and is impossible to answer based on the information you have given. There are tons of tutorials out there (youtube, etc.) that cover rendering in Revit.
Do you have a specific rendering issue that's causing you problems? Can you elaborate on what you've tried so far, and perhaps provide an example of what you hope to achieve?
You can begin reading lessons from AU (Autodesk University)
Some example of Classes handouts on this subject:
AB 4025
AB 4267
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from Rendering >Quality >Setting >Custom (view soecific) >Edit > Render Quality Settings....
Pay attention to thiese settings....at high values the rendering can last hours...
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To have a higher resolution -