Not sure what your showing in, but I presume it would be the same as im used to.
The judge will tell the first person what to do, and you just watch that. If you have any questions ask when its your turn, just before you do your workout.
Usually you will be asked to walk out, trot across the back, halt and stand her up square, then trot back.
You could be asked to halt in front of the judge or trot passed. Sometimes you are asked to walk out, halt, then trot the rest also.
If your asked to do the second of the above, make the second corner (i hope this is making sense) like a semi circle, its heaps easier to turn and looks alot better than fighting with the horse and trying not to trip over at the same time