When we apply a small horizontal force F to the right side on the block, the block does not start moving from its position. See figure (C)
Now, the force F applied to the block by the floor of the table bends to the left so that P, mg, F form a closed triangle. Force P can be divided into two components.
Parallels and verticals of contact planes. The parallel component of the contact planes is called force of static friction (fs).
And this balances the applied force F. There is a normal reaction R on the block perpendicular to the contact plane which balances the weight mg of the block. (R = mg)