Some modules have textbooks, others have only online materials. There are usually online tutorials and activities, and forums for support. You get a tutor you can contact and who marks your work.
The modules are structured, with study calendars and timetables, and assignment deadlines.
You're not just left completely on your own lol.
At the end there is either an exam or an End of Course Assessment which is like a project or big assignment.
If you want, pop over to the thread in Groups and Discussions > General, there is an O.U. thread in there.
Good luck