Raycast chase player, avoid walls.. raycast detailed C# tutorial?

I have read a bit on raycast(mostly the docs), and I know how it works, but I only know the very basics. I want to learn more about it. My question I was using it yesterday, I want my object to chase a player, but avoid walls, and not chase my player if it's seen through a wall.

I think a detail tutorial would help me with that. I have tried reading the docs, but without examples I am a bit lost.