Ok, here's a little explanation of what Geocaching is.
You go to the www.geocaching.com site and put your zip code into the box on the top-right of the page to find caches near you. Then you try to go find them using the latidude and longitude given in the cache listing, usually by using a handheald GPS unit.
All caches will have a log to record that you have found it, but the larger caches will have some trade items in them. The idea here is to sign the log to record that you found the cache, and if you want to take something from the cache, you leave something of equal value. The caches are sometimes small matchstick containers that have only a log, but may be as big as a 5 gallon pail. Most caches have toy items, or something similar, and this is a hobby of many families, as the kids have a fun time finding the cache and sorting through the items. After you find them, then you record your find on the geocaching web site.
That's all there is to it...until you realize that most GPS recievers are good to about + - 15 feet(in the BEST of conditions), and the cache could be anywhere in that circle. In the middle of a woods in the summer, with leaves on the trees, you might have 50-100' accuracy or worse. Of course, mosquitoes, poison ivy, briars, snow and ice also add some excitement to the hunt...
For me, I was told I had to get out and walk more, so this is a way to get out into the parks and other areas. A lot of the caches are placed in out of the way areas that might be easy to get to, but you never knew existed in your area. I've found a bunch that way, as well as having to walk a mile or more to find some.
Quite a few places have area clubs that can help you also. Check the web site for more info on those...