The definition of public opinion is defined as the aggregate of individual attitudes or beliefs shared by some portion of the adult population. There is no one public opinion because there are many different types of "publics", (American Government and Politics Today: The Essentials; Bardes, Shelley, Schmidt.)
Public opinion plays an important role in our political system, just like it does in democracy. It started out by Americans willing to express different opinions on political issues. This is started through a process called political socialization, meaning in other words people gain their political beliefs and attitudes through their families, friends, teachers, co workers, environment etc.
Public opinion affects political processes in many different ways. The president, members of congress and other public officials realize that public opinion polls make a huge difference in their careers for example if the opinion polls are suggesting that they do not like the president or the governor than that would make them look really bad.
This deeply impacts the shape and direction of their campaigns.
Therefore, in the end public opinion is very important today because it can lead to many bad or good campaigns in politics, and we shall try to keep on improving this by speaking out to others, and making our voices heard.