In this answer, I will say a little about myself, but I will also try to give you the ability to answer this question on your own. It is important that you answer it on your own because the social forces that affect you are surely going to be different than those that affect me since you and I are presumably at very different points in our lives.
We human beings live with lots of other people in our society. We have relationships with those people. Those relationships put certain types of pressures and expectations on us. We (at least sometimes) feel the need to act in the ways that people want us to act.
For me, the only real social forces that impact me are the expectations of my employers and of my family. Because I need to make money, I need to care about what my employers want me to do and how they want me to behave. I want my wife and my kids to continue to love and respect me. This makes a big difference in how I conduct myself every day.
But this question is about you. What pressures affect the way you behave? Do you belong to a church that matters to you? If so, that might be a social force. Do you watch a lot of TV or movies that may affect your views as to what is cool and appropriate? Do you care a lot about what your friends think of you? All of these things are social forces that may be important to you. Try to think about these questions and about anything else that might affect you in your life and write an answer that will reflect your reality.