To understand what is the social construction of reality, looking at the source of the idea in sociology provides a clear understanding. The reality of the world is not something concrete but a product of social interactions between people. Reality is what people chose to make of it meaning that people define their reality. Through daily interactions between humans, meaning is attached to elements that make up a society such as culture, language and other aspects. As people interact with each other, they fall into habits and start drawing lines on what is considered normal, by doing this people construct a list of societal expectations that are adopted by all members of the society.
The conduct of a person in a religious building such as a church is a good example of the social construction of reality. A church is just a building but if you consider the meaning attached to it, church-goers are expected to behave in a certain way based off what members of the community regard as proper. The expected code of conduct in a religious setting shows that this reality is constructed based off shared meaning attached to it. By observing how individuals agree on what is proper in such a setting you see how reality is constructed by society.
A key element of culture such as language has meaning to it because it is a shared tool among members of a society. Language works because it is a popular tool since members of a society agree on the grammar and semantic denotation of words within it. This shared understanding of a language is a product of social construction and shows how a tangible tool such as language is not something real but a construct of interaction between humans.
Proving that reality is not static but something that is evolving can be achieved you can explore the concept of money. In earlier days, humans depended on the barter trade to acquire goods and services. This method of doing business was unreliable necessitating the need for a common currency to do business giving rise to the idea of money. Cowrie shells were the first items to be used as money before the paper currency was introduced. Paper money is just pieces of paper, when you consider the value attached to it, money becomes more than pieces of paper. The concept that a piece of paper has certain value attached to it proves that reality is a social construction.