Hmm. I would imagine that the phrases mean the following:
I think this relates to what level of education you want to obtain from the institution you are applying to. This might be a Bachelor of Science or Arts (probably Science in the case of Sociology), a Master's or a PhD.
Goals of Study
This is asking what you want to gain from your studies from the institution. These could be increased knowledge, personal growth, useful job skills, information you can take back to Cambodia, or other such things. You want to be as broad as possible to show the institution that you have a wide range of goals and interests.
This is probably Sociology for you. You would need to specify what parts of Sociology appeal to you and why. You might also want to include other academic areas that you are interested in and why to show the institution that you are a broad-minded person.
You will probably want to wait and see if anyone else answers your questions, so you have multiple opinions. This is obviously very important for you!