Halter is great, I loved it, so much so that I got heavy into showmanship as well. Its pretty easy to do, but its complicated to explain here. If you have someone that can give you a few hands on lessons, that would be best. Or even go to a few open/schooling shows to help gain the info you need.
Your horse will need to be able to follow in a straight line, stop straight, back straight. Stop with all four feet squared, eventually they will start to do this on their own. Pivot on hind, keeping the outside rear hoof in place, keeping the body square. Trot off with you and stop with you. And then you will need to learn quarters, split horse nose to tail for one half, then shoulders forward is one quarter and shoulders back the last. You need to stay one quarter away from the judge. If they are looking at the left butt, you are on the right fore, they cross to the right butt, you cross to the right front. You only need to stay in 2 spots and be able to walk in front of the horse but be close enough for control.
Now this info is for QH shows, I dont know how you will be showing. As you can see, it can get pretty intense to explain. Hopefully you can have someone give you hands on help. Oh, forgot the most important thing! S M I L E !!!!! Even if you booboo, no biggie, keep on a grinnin!!!!!
Forgot to add about trimming and cleanliness. For that you will need your breed specific info. But that horse needs to be perfectly trimmed and clean to a shine. I used to pull my manes and tails, and banged the tail just a tad. I didnt do all the banding etc, kinda like the natural look LOL now the big thing is dyes and fake tails, to me, thats cheating