After importing the post-processing stack in your project you have to add a Post-Process Volume to your scene. This Post-Process Volume will determine what effects will be used within its volume.
Create an empty Game Object and add a Post-Process Volume component to it. Then enable ‘Is Global‘ to make sure that the volume is used for the entire scene.
Furthermore, the volume requires its own layer in order to work correctly. Click the ‘Layer’ button on the Game Object and choose ‘Add Layer’. Pick an empty layer and type ‘Post Processing’ to create a new layer for post processing. After adding the layer, go back to the Game Object and select the ‘post processing’ layer.
Now that we have a Post Process Volume in the scene we have to make sure that the effects are applied to the camera.
Select the camera that you want to add the effects to and add a Post-Process Layer component to the camera. Next, choose the ‘Post Processing’ layer in the ‘layer’ property. This will make sure that the correct volume is used.
Finally, we have to choose which effects to use. This can be done with a Post Process Profile. Select the Post Process Volume component and pick the ‘PBR Neutral’ profile in the ‘Assets/Open World Nature/Common/PostProcessing Profiles’ folder to use our included profile with all effects set up.