Take a look at the diagram below. It shows the forces exerted by Michael and Jack as they try to move a piece of furniture. Michael is exerting a 40N force at 45° and Jack is exerting a 30N force at 0°. Together, they are exerting a total force on the piece of furniture.
In order to find the total force exerted by Michael and Jack, we need to resolve their forces into their x and y components.