If you are including the steps of writing the patent then, as Eric Shain posted, the answer is at least book-length. The book Patent it Yourself is a good start. If you are asking just about the mechanics of filing, that is a shorter answer. If that is the question, I would suggest that you edit your question or submit another question.
Taking the question more broadly - the USPTO has a reduced fee schedule for what it calls micro entities. The primary way of qualifying is based on income. Most fees are cut in half from the fees for "small entities". They also sponsor a pro bono program that might match you with a local patent attorney who could work with you at no charge. They do not take everyone who applies.