When you are going to write a master's thesis, you will need to find a supervisor. She or he will be responsible for guiding you through the process of writing your thesis, by helping you with aspects such as choosing a subject, formulating research questions, and analysing the data. Of course, supervisors only guide you, which means they will help you, but not do the actual writing for you.
When you speak to your fellow students you will soon find out that no two supervisors work alike. Good communication is critical! Make sure that you know what is expected of you and what you can expect of your thesis supervisor.