Buy colts or geldings with at least one E or above. P's can do well, but you have to be more experienced with how showing works first. Geld any colts. You won't be breeding your show horses, though you might want to show your breeding stock.

Plop a rider on, train in their E discipline if they have one or in all events for the first 5-6 weeks until you can see if they are strong in one show type's stats or you want to show them in all types. Once they've had 5 weeks of training, show them. If they place 7 or better, good. If not, don't enter them again that week, wait for the next week. When they level, wait another 5 weeks to show them again.

That's the barebones outline. For a really good guide on how to show once you've got your geldings bought, look in the Guides section of the Member Help forum and find Eury's magical, totally awesome showing guide.

Because there's a gap between levels, it's a good idea to have a few weeks' worth of geldings to show. I mean if you buy a few foals every week you'll have someone to show all the time once they start placing.