Merriam Webster defines popular sovereignty as "a doctrine in political theory that government is created by and subject to the will of the people". In a simpler term this means that the people are free and the government receives all its power from the people.
One of the Best examples of this is contained in the first three words of the constitution, "We the People". This meaningful set of words states that we are a group of people, no matter where you come from everyone is equal. This sets a basis for how the government is run. Nobody is above the government and the government is above no-one.
One other example of how we show popular sovereignty is through the process of voting. Citizens vote on who is going to represent them in the government. They decide who has similar ideals and beliefs and once they are in office, we expect them to do what we want. We also vote on laws. We decide how the government should treat us, and those around us. We have the power to voice our opinion of how the government uses their power and what actions they take. All of this gives us power and makes us equal to the US government.