Here’s the rendering equation:
And here’s me trying to understand it:
It’s the integration part I don’t get. I know what integration is, and I know the basics of using it, but what does it have to do with anything? I know the omega subscript indicates that the integration has to be done over a hemisphere, but what does it mean for integration to be done over a hemisphere? Where am I? What is life? I don’t understand what’s going on 
I get the rest of it. But why is it an integral equation? Thanks 