Refine Edge tools

Hello all

Can anyone let me know how these tools work in the "Refine Edge" options.

• The select/deselect icons on the top left
• The smart radius option
  
• Does the radius slider work in conjunction with either of these?

 I have watched youtube videos etc but still don't seem to be able to make them work as expected, so I must be misunderstanding something.

When I use the icons to fine select hair for example, the results seem very random.

Any links, guidance etc. will be much appreciated.

Thank you.