The sun provides the earth energy in the form of raditaion and heat.
The sun is the source of energy that fuels plant growth, forms the base of the food chain, and warms the air in the atmosphere which influences the climate.
What are the effects when it changes?
The amount of energy coming from the sun does not change enough to change conditions on earth. However, the angle or distance of the sun from the Earth can change making it warmer or colder depending on the angle or distance.
Can humans alter this factor or process?
Nothing influences the sun because the sun influences mostly everything.
Humans cannot influence the sun because the sun cannot be influenced by humans. The sun is a star so it can only be influenced by its own fusion of gases and itself.