You may wish to read these other notes to reinforce the material here. You might also like to take a look at Science for all - science for none , in which I reflect on why science is seen by many as a difficult topic and suggest ways of approaching the teaching of science. Forces include pushing, pulling and twisting.
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.