Hi Debra,
Pin trading is terrific activity, and it's very easy to get started.
Your first step is to buy some pins. You can do this at almost any shop at Disney World, Disneyland, Disney Store, Disney Cruise Line, or on sites like eBay. The only pins that are officially allowed for trade are ones with a Disney logo on the back, so be careful if you buy from a non-Disney location.
For trading in the parks, most folks wear their pins on a lanyard, but you could also use a had, jacket or vest for display.
To trade, you simply walk up to a cast member (or another guest) and politely ask if you can see their pins or if they'd like to trade. It's really that easy. Cast members will say yes virtually all the time. Take a look at their lanyard. If you see one you like, offer one of yours in exchange. Other guests might nicely reject your offer, but cast members will usually accept. Then you just switch pins.
There are many thousands of pins out there. To narrow their focus, many guests try to collect to a theme. For example, you might collect only Minnie Mouse pins. Some guests collect pins representing a particular film, resort, ride, or event. They choice is really up to your interests.
Have a great time trading!