Level 3 is A Level or equivalent.
There is a distinction between studying Computing, Information Systems (IS), Information Systems and Technology (IST) and Information and Communications Technology (ICT).
If you want to study at home, in your own time, just buying (or borrowing) and working through a text book might be enough.
Students often donate or sell their books after exams are done so you might find something in a charity shop or online.
Bear in mind that some Year 1 material on Level 4 undergraduate courses may be of interest. Take a look at free Open University courses. Look for course prefixed T or M.
www.open.edu/openlearn/free-courses/full-catalogue
It would help to know more about what you want to learn. If it to become more confident in using general purpose computer software: word processing, speadsheets, presentations and databases, you might find the International Computer Driving Licence (ICDL), formerly the European Computer Driving Licence (ECDL), helpful but again you could learn all this from a text book:
www.distance-learning-centre.co.uk/european-computer-driving-licence-ecdl-online-course/