Using Layer Filter Raycast

In Unity videos, I have found that using layer I can able to filter raycast hit. This is one of the usage of creating layers. There are little talk about that in that video. So I can't able to understand how to achieve similar thing?

I know about how to set visibility of game objects using layers. In camer, I have to set which layer I want to view. Basically I want to ask that how to create game object that does not affected by raycast hit using Layers?