what are contact forces and according to: https://www.physicsclassroom.com/class/newtlaws/Lesson-2/Types-of-Forces
it says there are 6 types of contact forces. I am having doubt with applied force and normal force because both acts when there is contact between two bodies when we push a book kept on a table we take normal force from table surface, but what about the contact between my hand and book we say that applied force, when we push a wall horizontally we say its reaction force is normal force but how ?? when we kick a ball we say we applied a force but where is the normal force between my foot and ball surface which came in contact during kicking, or when we hit a ball by a bat we say we apply a force with bat on the ball but what about normal force between bat and ball surface. when we pull a string attach to a celling we say we applied a force on the string but what about the contact between my hand and string surface where is normal force between them. i am so much confused please somebody help me with this.