How do I write a discussion for my internal essay in psychology?

You should start your discussion by re-stating your hypothesis and making it clear whether your data have or have not supported your hupothesis. You then proceed by stating your results and explain how your results have either challenged, contributed or extended scientic knowledge in relation to your research question. How to your findings help improve the understanding of that specific field? Are your results in line with previous research, thus validating previous ideas on this topic or are they contradicting previous findings that shreding light into new possible theoritical and empirical theories and ideas? 
Once you have explained and compared your findings you have to address prossible limitations. This means that you need to identify possible aspects of your research that could have influenced negatively your results. For example, unequal number of males and females, using a specific nationality of age range etc. However, your limitations should also be explained using previous research. You cannot state that using more males have influenced your results unless previous research has shown that there is a different effect on males and females. 
Once you have written your limitations, you shall write your future recommendations. What do you think would be beneficial to improve research in your topic area and how this would be achieved. Once again comparing your ideas with previous findings could be a bonus.
The last section of your discussion is your conclusion. This is a small paragraph in which you summarize your hypothesis, findings and future recommendations.Bonus tips1) Most of your references should be studies conducted within the last 5 years as older research could have now been falsified. Do not forget to always reference according to the style your school has chosen.
2) Do not repeat your introduction.3)  Try to use more than one study when comparing your findings as this not only shows your knowldege but also validates your arguments.