A force is a push or a pull that happens when two objects interact. Some interactions need the objects to touch. These are contact forces. Friction is a contact force that acts between surfaces that are sliding, or trying to slide, past each other. It acts in the opposite direction to the motion. The normal contact force is the push a surface gives to an object resting on it. It acts at 90 degrees to the surface, which means it is perpendicular to the surface, so the table pushes up on a book lying on it.
Other interactions work across a gap with no touching. These are non-contact forces. Gravity pulls any two masses together, such as the Earth and a falling apple. Magnetism acts between magnets and magnetic materials, so a magnet can pull a paper clip through the air. Electrostatic forces act between charged objects: like charges repel and opposite charges attract.