There's a good starter's guide here - http://www.geocaching.com/about/default.aspx . The 'caching community is incredibly friendly and helpful. If you'd like to add me as a friend on geocaching.com I'm Purplebint there too.
I currently use the app on my Iphone but I'm starting to look at dedicated GPS units as battery usage can be an issue.
We spent this morning geocaching in Bradgate Park. We're very lucky to live so close to such a beautiful place and it's been one of my favourite places since childhood.
Here's some photos from our trip out this morning. We planned to find two caches that were relatively close to each other, however there was a herd of deer enjoying the shade in the copse that contained one of the caches so we left them to it and will return another day!