Shaz asks:

“What is resultant force?”

Answer:

When a number of frces are acting simultaneously on a body, it will be producing an effect – may be keeping the body in equilibrium, or giving it an acceleration in a particular direction.

Resultant of a number of forces is defined as that single force which can replace all other forces to produce the same effect.

If the number of forces acting on the body keep it at rest or maintain uniform motion,it is said to  be in equilibrium; then the resultant is zero (since acceleration is zero).