Before you begin, make sure you know the word limit for your essay. You will usually be given a definite number eg 1500 words or 2000- 2500 words. If you are given a fixed number, it is usually acceptable to write 10% fewer or 10% more words. If you are given a range, try to stay within that range. However, check this with your tutor as you do not want to be penalized.
If you do not know how to write an essay, going back to college or starting a university course can be a daunting prospect. If it is years since you have done any type of studying, let alone essay writing, do not worry - most colleges, including online universities - have study skills information, including homework study tips and essay writing guides.