Understanding how multiple shaders are used

Maybe I misunderstand this, but lets say I have a scenario where I want a Toon shader, a shader that makes my model glow, and a shader that creates an outline around my model when its selected.

1. Is this achieved through using one shader, or several?
2. If I want to for example toggle the selection outline on/off during runtime, how is that done?
   

 

1 Depends on realization.
You can use several materials with one mesh renderer, or you may switch additional effects inside one shader.
2 It's also depends.
2.1 Renderer.materials
2.2 Material.SetInt or Material.SetFloat
2.3 Material.EnableKeyword and Material.DisableKeyword(https://docs.unity3d.com/Manual/SL-MultipleProgramVariants.html)