These two effects are not too complicated and can really make the 3D scene look much much better. For a simple 2D texture, it can turn something like this :

photo

To :

photo

The effect simply consists of displacing the texture coordinates of the rendered texture depending on the angle at which the camera views the surface.

The best explanation I found from here : https://learnopengl.com/Advanced-Lighting/Parallax-Mapping