The first thing to do now would be to go along and watch a dog show. See how the people there show their dogs and just feel the atmosphere. Talk to people at the show (so long as they are not just about to go into the ring

;) ) and see what happens.
Ringcraft is very helpful for people and dogs alike. Especially if you haven't done it before. The people there should be able to help you. Let them know that it's your first time showing your dogs and they should give you some basic help. If you can find someone close to you who show the same breed as you they might be willing to help you.
Now that he is over 18 months old he will have to go into the first available class after Junior. Different breeds have different classifications so you would need to check with a schedule. I would start at Open shows. They are usually closer to home, cheaper and have less people and dogs attending.