This issue of copyright is so tricky, and I have heard so many conflicting opinions. I found this article on the internet, written by a woman who is a quilter and also an attorney specializing in intellectual property. I know - you can find ANYTHING on the internet, and you don't know which articles are factual and which aren't. However, these rules make sense to me, so I intend to follow them.
http://www.quilttownusa.com/Town_Hall/cpexperts.htm
To paraphrase the article, if you buy a pattern you may make the article in the pattern, and sell this article or give it away, and you may sell or give away the original pattern. (You paid for it, you own it - the pattern that is, not the copyright.) You may also make the item in the pattern and use it as a raffle quilt.
You cannot mass produce the article in the pattern for distribution, and you cannot make copies of the original pattern to distribute to others. A copy of the pattern for your personal use is allowed. (I would assume that if you make a copy while you own the pattern, then you should destroy that copy if you sell the original pattern, or give it to the person who receives the original pattern.)
The article doesn't address showing your quilt, but I can't believe that anyone selling patterns would discourage that activity, or that it would be illegal to show something that you legally made, having purchased the pattern (or having been given it by someone who did purchase it). It is good manners to give credit to the pattern designer when the quilt is shown.