A book on a table
Take a book placed on a table. Gravity acts downward on it, and yet it does not fall to the floor. Why?
Figure to be added
Here the weight of the body acts vertically downward, and that force is balanced by the normal reaction the table top produces vertically upward.
Normal reaction
The force a surface applies perpendicular to a body placed on it is called the normal reaction.
R = W
For a body at rest on a horizontal surface only.
Under those two forces the book is in equilibrium on the table, and the body stays still.
How can a table apply a force?
It is easy to think a table cannot apply a force, not being alive. But the weight of the book bends the table top by a very small amount, and its effort to straighten again pushes the book up. A heavier book bends it further, which is why the reaction always comes out equal to the weight.