Where can I find those visual effect demonstration? I'm studying Unreal Engine, this chapter is talk about visual effects: Rendering Overview

Some of them has obvious picture I can see whats the differences. But not all of them. Is there a site can let me input the keyword, like 'bloom', then it shows the description, a image contains 'no bloom' and 'has bloom' both?
The Unreal Engine documentation has good explanations for their various post-processing effects like Bloom. You can find more information about it here: https://docs.unrealengine.com/en-us/Engine/Rendering/PostProcessEffects/Bloom

In the case of UE4, bloom becomes observable once color values push beyond the 1.0 value.