1. Leave the main search field blank. That field is only used when searching around a single point, which isn't what we want to do here.
2. Enter the portion of the cache name you want to search for in the "Geocache Name Contains..." field. To choose which region to search within, click in the "Search Only In..." field and begin typing the name of the region. Once you see the desired region in the suggested options, click it. Click "Search" to apply these filters.