Chapter 4 Blog

I understand that a market is filled with buyers and sellers.
I believe that competitive markets are everywhere and there will always be a competitive market.
I don't understand how a Perfectly Competitive market is possible.
Would Monopoly be similar to an absolute advantage?
I'm not understanding fully the demand graph.
Would a consumer be considered a third party effect?
Would substitutes and compliments be related?
Can you explain the Supply Curve?
I understand pretty much all the rest, especially the Law of Supply and Demand.