OK let me see if I can help you with this one. I have about 25 pins or so in my pin collection but DH started collecting on our first trip in 1999 and he now has several hundred and spends hours pin collecting on each trip.
We started our collection out by buying 10 pins at our local
Disney store before our trip since the Disney store pins are cheaper than the pins you can buy in the parks. Another way that DH gets some of his traders is to buy on E-bay. You can often get several of the "rack pins" on Ebay for cheaper than you could buy them in the parks.
You then put your pins on your lanyard and you can trade with CM's or guests. CM's are required to trade any Disney pin for anything you want on their lanyard...no begging required (One exception was that on our last trip you could not trade a CM for a pin they already have on their lanyard...it used to be that some poor CM's would have 8-9 of the same pin on their lanyards). Guests are not required to trade with you and begging can be involved in those transactions depending on what pin you want.
There are a million (well maybe not quite
) different pins for just about everything - characters, resorts, rides, special events, etc.. There are standard "rack pins" that are unlimited in number but there are also limited editions, cast member only pins, etc. The LEs and CM pins are often times more highly prized and you will not see too many of them on CM lanyards.
DH and I are pretty casual pin traders and we just trade for fun. We only collect certain things that are of interest to us. I like Dalmations and Eeyore so I have several of those pins but I also get a pin for each resort we stay at or a pin of a ride we really enjoy, etc. My DH collects Disney mice other than Mickey and Minnie (especially Timothy Mouse but also the Rescuers, Great Mouse Detective, etc.).
I hope this helps. My biggest tip is to just have fun with it. Enjoy the time you spend talking to the CM's while you trade.
Feel free to PM me if you have any other questions.