An Introduction to Geocaching
In order to get started in Geocaching, we suggest that you read through the excellent introduction hosted by geocaching.com. But if you prefer, here is a brief summary - which is neither comprehensive or complete - but may well be enough.
First, and above all else, you will need a GPS receiver. Most any unit will do, but at the very minimum it is recommended to buy a modern unit, don't get a second-hand unit if possible. Most new receivers also support WAAS, which if you live in North America, means you can get far superior accuracy - which is always a good thing. If you have lots of money, then by all means, get yourself a top of the line GPS receiver with all the bells and whistles. However, most any GPS receiver will work just fine. I do, however, highly recommend purchasing a unit that uses the MediaTek chipset (for example, the Garmin e-Trex H series), which is far more sensitive than other chipsets currently on the market.
Why? Well, Geocaches are often placed in wooded areas or locations where a clear view of the sky isn't always attainable. This chipset is quite sensitive, and is often able to maintain a lock in unfavorable conditions where other GPS receivers cannot. Garmin offers some units that use this chipset, often designated as "high-sensitivity". I personally use the Garmin eTrex-H series; these are low-cost and very high sensitivity receivers, and I have had very few issues with any of the devices I have purchased.
Some advice regarding the GPS chipsets: There are several companies marketing different chipsets, and most (if not all) modern GPSs use a quality one. Technology is improving all the time and what might be the best today will most certainly be superceded by something better in the near future. As of this writing (2011) the MediaTek chipset is about the best you can expect to find in a commercial handheld receiver, but if you are serious about buying a quality GPS receiver for geocaching (or any other purpose for that matter), be sure to do your research before making a purchase.
Also, it should be noted that most GPS receivers now come with a data sync cable, which is almost always a universal USB cable. However, If you purchase a used GPS, you may need to buy or build a serial GPS cable for it (I built one for about $5 using connectors from pfranc). You can read more about the cable and the built-in voltage regulator here.
The next thing you will need to do is to sign up for an account on one of the geocaching websites, this is free. Although there are several alternatives, the original and most popular geocaching website is geocaching.com. Once you have signed up, read as much as you can to learn as much as possible about Geocaching. Most - if not all of these sites - offer a significant volume of material on Geocaching, rules, etiquette, guides, forums, etc. Then, do some searches and find some caches in your area. It's best to start with an easy cache, something nearby with a a low difficulty rating and preferably a traditional cache. Start small. Take your GPS, either enter the coordinates manually or download them to your unit with the data cable before you go. Then go find that cache!