http://www.bbc.co.uk/webwise/ A beginner’s guide to using the internet, also with a section on computer basics.
http://www.homeandlearn.co.uk/BC/BeginnersComputing.html#win also has tutorials for beginners.
http://www.learnmyway.com/ This site is provided by UK online centres to give new internet users and tutors in computer centres a range of easy courses and useful resources.
http://www.gcflearnfree.org/computers is a very useful site offering a wide range of computer training.
I haven’t yet written about ‘social media’ sites, so try here http://www.bbc.co.uk/webwise/courses/social-media-basics/ to get information.