The main cache listing site is Geocaching.com. You'll find over 9,000 caches in the UK listed there. In order to see the full details you'll need to register, which you can do free on this page.
Then go to the "Hide and Seek a Cache" page, where you can enter your home co-ordinates or your postcode to find caches near you.
Caches are rated for difficulty and terrain - you might want to try a few with low difficulty ratings first. Look for Traditional caches - a traditional is a single hidden container. And look for regular size ones as opposed to micros, which are very small containers, often 35mm film canisters, which can be much more difficult to find than a "regular" tupperware box or ammo can.
Happy caching!
Do not go gentle into that good night.
Rage, rage against the dying of the light. (Dylan Thomas)