Hi Penny,
I'm pretty new to pin trading too, but I'll try to answer some of your questions.
Yes, these are the pins that people wear that you can get at the
Disney Store. They can also be bought at all the parks, Downtown Disney, on the cruise, etc. Some pins are exclusive to the park where they are sold and so, people who can't get to that park, trade for them. To be tradeable with the CMs, they have to be an official Disney pin with the Disney copyright on the back and of the cloisonne variety - that is, the hard metal enamel type, not buttons, etc.
It is both a child's activity and an adult's... though some people get way overzealous about it and can be a little scary. I've always been told that if you don't feel comfortable with a trade, simply walk away. There is nothing obligating you to trade with someone or for something you don't want to trade for.
The exception is the CMs. If they are on duty and wearing a lanyard, they are required to trade any pin on their lanyard for any Disney copyrighted cloisonne pin that you offer them. The only way they can refuse is if they already have the same pin you are offering them on their lanyard. The lanyards are simply a way of people displaying and wearing multiple pins. It also signals to other traders that you might be open to trades, although, as I said before, you're not obligated to trade if you don't wish to.
HTH,
Julie