A doctoral candidate has an adviser who works with him on his PhD. This is an academic who will closely work with the doctoral candidate to ensure that his research is sound and his topic is relevant and who will give suggestions and advice as to how to produce his dissertation. It is the student's responsibility to choose his adviser; more important, he needs to choose his adviser well. The doctoral candidate needs to research a potential adviser's past work to ensure that it matches his areas of interest. He also needs to check to see what a potential adviser's availability is like during the term of his PhD (does he, for example, have a sabbatical coming up?) and speak to people who have worked under him in the past to see what his advising style is like.
A PhD student is responsible for completing all of his classwork to a high standard. Doctoral programs are not like undergraduate programs --- they do not tolerate failed courses. Since half (or less) of all doctoral students ultimately graduate with a PhD, it is the responsibility of every student to deliver extremely high-caliber academic work during the first couple years of the PhD. Basically, your coursework is your opportunity to show your ability to perform academic work --- you need to generate high-quality, well-researched papers that show your ability to research, synthesize and articulate other academics' arguments, create your own arguments and defend them at a complex level.
Some PhD programs involve fieldwork. As with the rest of the PhD program, these are self-directed. Candidates are responsible for creating a fieldwork plan, writing what they expect to achieve from their fieldwork and following through with it. What's more --- and arguably most important ---candidates are responsible for informing themselves as to their university's ethical guidelines and following these guidelines during their fieldwork.
Many doctoral programs --- such as the University of Toronto's Anthropology Department and most history departments --- give their students the responsibility of learning a second language. The reason for this is because professors need to be able to participate in the international academic community. What's more, many documents and articles are often written in different languages. Learning another language opens up your access to information, thus allowing you to produce better-informed work.