When studying a PhD, you will carry out a piece of research independently though under supervision. As the work is conducted independently, some people find it an advantage to complete a more general, taught, introduction to research first, such as a Masters course. You will carry out all aspects of the project: literature reviewing and designing the project, ethics application, data collection and analysis.
You will review your work with your supervisors regularly (e.g. monthly) and they will support you at each stage while also continually challenging you so that you develop your skills of critical analysis and are able to defend your thesis.
Institutional requirements for progress reports will vary; usually there is a minimum expectation for an annual report. Most institutions expect that you enrol on an MPhil/PhD and you then prepare a proposal for registration. Later in your studies, you transfer - or 'upgrade' - from MPhil to the PhD pathway when you have made sufficient progress to show that you will be able to produce a doctoral thesis. This is likely to require a report of your progress, the expected new knowledge and a plan for the next stage. There is a growing expectation for PhD students to publish peer-reviewed journal articles and present their work at academic conferences during the course of their PhD.
The expected thesis length is usually around 80,000 words (excluding reference list and appendices) but there is some variation in institutional regulations.