Normal force is a contact force.
It is the force that surfaces exert to prevent solid objects from passing through each other.
If two surfaces are not in contact, they can’t exert a normal force on each other however, if they are in contact, they exert normal force on each other, perpendicular to the contacting surfaces.
Take an example of a book on the table. The normal force on the book is equal but in opposite direction to the gravitational force applied on it. This is what causes absolute no movement upwards or downwards. Therefore, here we can say that the normal force from the table surface is equal to the weight of book. This only applies where there is no outside forces at work.
For an inclined surface,
Theta(θ) is the angle of inclination.
Consider a box on of mass 2 Kg placed on a surface inclined at an angle of 15 degrees.
Therefore, the normal force is 18.93 N.