Gravity is a force, so too is friction. Forces act to move an object, to accelerate an object, to slow an object down, to make an moving object change direction or to keep it at rest. Forces can also be used to change the shape of an object - such as blowing up a balloon or crushing a can. Two or more forces can be in equilibrium, that is balancing each other. When a ship is moving at constant speed it does so because the forward motion caused by the propeller is balanced by the friction of the boat through the water.
Friction acts in the opposite way to the direction of travel.
If there were no friction then, provided the propeller kept turning, the ship would continue to speed up. Alternatively, once moving the propeller could be switched off and the ship would travel at a constant speed until some other force acted upon it. If we continue with the example of the ship then there are other forces in balance. It might be easier for children to understand balancing forces when you use the example of a see-saw. Children will position themselves at different points on the see-saw to balance each other.