Distinguishing real forces and fictitious/pseudo forces in Newtonian mechanics

In understanding the law of inertia I had to consider the motion of bodies screened from the so called "real forces".

• 
  

  What characterises these real forces?

  
  


• 
  

  What makes us call them real?

  
  


• 
  

  Or what is separating the forces called true or real from another group of forces called fictitious/pseudo forces?

  
  
  

Many forces called true are also invisible just like the centripetal force or other pseudo forces.

• Then what is making them special and different?