I have a new show jacket for WP that's sort of military style. It's a bit short like most western jackets, so there would be some gap between the jacket and the top of the chaps. What do I wear underneath the jacket?
Also, I have a belt that goes with it. I'm sort of new to WP and stuff, so how do you wear it when you have chaps? Do you put the belt over the top of the chaps?
Belts go in the belt loops of your pants and your chaps go over the top. The front buckle of your chaps will likely fall just below your belt's buckle.
Under your jacket, wear something fitted that matches your jacket, or otherwise doesn't draw any attention to the area - you don't want bare skin showing, nor a too-big shirt ballooning out the bottom. If your jacket & your jeans are dark colors, wear a dark under layer. If your jacket is a mix of colors, wear a solid under layer in one of the darker or most prevalent tones (light colors attract light & attention, so I always err on too dark versus too light - in everyday dressing, not just horses showing!)