what is a theory and how do you write one
From an accumulation of data in a specific area, a potential explanation for this data can be developed. That is a theory. The theory can then lead to specific hypotheses, which need to be tested. If the new data support the theory, it is maintained. If not, there is a need to modify the theory.
For example, there are several theories about the progression of human development.
What area do you want to consider for your theory?