What is a ring show? You mean conformation?
For all AKC stuff you need to have your dog's registration. You generally have to be registered/signed up for the show like 3 weeks in advance. There is a show closing date. UKC stuff you can register day of, or earlier and generally get discounts.
The obedience, agility, rally, conformation trials have fairly strict rules that you should know before entering. The actual trial has a very organized order that you should know before you ever enter the ring. You should understand what you are and aren't allowed to do when it comes to your dog. For instance, in the AKC, if your dog leaves the ring without a leash on, you get NQ'd, which means you fail even if you did get a qualifying score. There are also very intricate rules on points and what's allowed which you should have some idea of. For instance, in the AKC, depending on what exercise you're on, you can give your dog "encouragement" and lose points, but if you give a second command, you fail.
In Schutzhund shows, the obedience portion is memorized, so you need to know that before you get in there since the judge will not give you any commands.
You should join a club, or take a class that is pointed towards whatever trial/show you're interested in. I'd be surprised if your trainer didn't know some of this stuff as a sign of a good trainer to me is someone that has titled/shown their own dogs in the area they claim to be an expert in.
What is "real world agility?"