Make sure that you know at least the names of the the parts of speech and of the tenses of the English verb. It will be useful to have some ideas of how the tenses are used; Swan will help there.2. What topics I need to study so to avoid confusion (English is vast).
Once again, the course providers are the best people to ask. I have found that Swan's Practical English Usage and the OALD have been indispensable throughout my career. Many beginning teachers find Raymond Murphy's English grammar in Use a life-saver.3. Any extra reference material required?
Ask the course providers. The structure of courses vary, so it's difficult to give a general answer.4. What the first few days will be like - what I have to teach, little information related to the first two assignments?
You have paid your course providers a lot of money. Make sure that they give you in good time all the information you need.