The first decision you'll need to make about horse shows is what level show you'd like to attend.
There are unrated/schooling shows that, while often run in accordance with USEF rules, are not governed by USEF and therefore there is more variability in the standards that the horses will be held to, the judging and course design will be held to, etc. If you have a good local circuit for unrated shows, these can be a great way to get experience as you and your horse are learning the ropes.
Then there are rated shows (rated by USEF and the USHJA), which can be rated B, A, or AA. This rating is based on the amount of prize money available, and as you move up in the ratings there is, of course, more prize money, but also typically more difficult competition and higher expectations about performance. Shows also become much more expensive as you move up to higher rated shows. At rated shows, not all the divisions themselves are rated divisions. So you can be at an AA show, showing in an unrated division. Unrated divisions are not nationally governed, and therefore there is more variability between zones regarding what these classes entail. Unrated divisions never have prize money. Most A/AA shows will have a division called "pre-child/adult hunters", which is an unrated division. These horses typically jump 2'6", but again as this is not a rated division, it's up to show management, so they could jump 2'3" or 2'9" instead. There are also C rated divisions, such as the Children's hunters and the Adult Amateur hunters, which go at 3', and A rated divisions, such as the Junior hunters and Amateur Owner hunters, which go at 3'6".
Another important distinction between classes is who is eligible to compete in them. "Open" classes, such as the High Performance hunters (A rated division), Baby Green hunters (unrated), are, as the name implies, open to anyone. They are often considered 'pro' divisions, however, because it is usually pros who are competing and winning in them. Then there are classes restricted to amateurs, with the name "adult amateur" always denoting a lower level than "amateur owner". Finally, there are classes restricted to Junior riders (under 18), and again a "Children's" class will be a lower level than a "Junior" class.
Often, people who are just starting showing, will go to unrated/schooling shows first, until they gain a level of competency where it makes sense to spend the time and money to go to a rated show (rated shows also run for a longer time than unrated shows). There are certainly classes available for people just started out at rated shows, however. People will typically only start out at rated shows if they ride with a show barn and their trainer exclusively does the rated shows, IME.
I'm on the east coast, but I think you should be (relatively) close to Thunderbird Park for shows, and depending on your goals/budget/etc you are probably within a reasonable drive of Spruce Meadows, if you wanted to trek into Canada. It would be worthwhile making a trip up there just to see the competition, actually! That'd be a great place to get the feel of really upper level competition, although they do much, much more jumpers than hunters.
I hope that answered your questions, rather than made things more confusing! Happy to clear anything up if you'd like more information, or I was unclear!