Look on the web site
www.agilitynet.com. They have a link that goes to an alphabetical list of agility clubs, so you should be able to find the ones nearest to where you live.
Most clubs will only take dogs over 12 months old and your dog needs to have basic obedience like recalls pretty well established.
I do agility with my show bred Cocker William. He's pretty reliable but not very fast (but neither am I, so we're well matched). I think working Cockers are usually faster, but perhaps not so easy to get focussed.
Find the right club and I'm sure you'll have a great time. I think it's one of the best things for really building up a good bond with your dog.