If you're still struggling with some of these ideas, you may want to have a look at the following resources:
Market structure: http://www.bized.co.uk/learn/economics/firms/structure/index.htm
Market failure: http://www.bized.co.uk/learn/economics/marketfail/characteristics/index.htm
More presentations:http://www.tutor2u.net/economics/presentations.html
Some quizzes to test yourselves on:http://www.tutor2u.net/quiz/economics/default.asp
and related notes: http://www.tutor2u.net/economics/revision-notes/index.html
Good luck!
