If the GC is the same as the 510 (which I believe it is) than the caches you have preloaded into the unit are in the USA somewhere. Depending on where you are from they are not really good for you (I'm from Canada, so they are useless to me and I deleted them).
You are going to have to go to the website (geocaching.com) and hook up your Explorist GC to tour computer than follow these simple steps..........
1. Go to a cache in your area that you would like to find
2. Click on the "Send to My GPS" tab
3. Than a pop-up window should appear, look for MAGELLAN and click that
4. Click download
5. Than another box should pop up asking if you would like to do "download a newer version", Click NO! (Because you already have the
newer version considering you just bought it)
6. unplug the unit from your computer, click the geocaching icon on the unit and look for the cache you just downloaded.
Now it should be there, hope this is what you were looking for. The Explorist series is really easy to use.