If you are writing a master's thesis, I would expect you to have a thesis advisor, and you should ask your advisor directly. Also ask for examples of recent theses in your department that were considered good work, and seek out actual journal articles in your field of study, and use them as a model.
Somewhere in your institution, someone will have a style guide for theses, at least for the mechanical formatting details. You will need to know how to format the references, how to number the pages, and how wide the margins need to be. While you are looking for that, you should ask if anyone has prepared any written guidelines to writing style.
Outside of academic journals, most authorities recommend against using the passive voice in expository prose because it is indirect, colorless, vague, and boring. However, in professional scientific writing, using the words "we" or, worse, "I," is seen as egotistical, subjective and opinionated. So, the passive voice rules; experiments were performed, data was taken, statistics were computed, etc. Find what is customary for professional writing in your own field and use it as a model.