I have been to several and the are so fun! Provided you go to have a good time and don'e expect perfection. Typically there are 8-10 obstacles, sometimes "judged" sometimes you just get score if you do it, not based on how you do it, etc. Anyway, the obstacles vary greatly. It would be really helpful if you are riding with horses who are pretty "bombproof" and willing as they will help to keep your horse going. Anyway. there is typically a "carwash" type obstacle-which can be many things, but I have seen noodles from the sides on posts to walk between and carpet or tarps cut into strips mounted above-you ride through. If your horse is resistant, try and get close enough to seperate it a bit for them and they will many times then go through.
There is typically a bridge type obstacle, something to walk in and back out, picking things up and moving them, dragging things-can be logs, bags of tin cans-hitting garbage can lids tied between trees, water obstacles of all sorts-last one we had a ditch dug by a backhoe (So it was narrow) filled with water to walk through, plus a pond to go through, balloons, mailbox to take mail out and "deliver".....
WE used to host them at our farm and had everything from goats to minis to girlscouts having birthday parties as you crossed a creek, to dirt bikes....strollers......
TO prepare for the last one, since it had been a while-I went to the dollar store and got balloons, noodles, flags, I had a tarp, we used cones to move from one post to another, used a rope as a practice gate.......and suirt guns we had to fill from a bucket on a barrel and shoot balloons........
Many many things you can do. Be creative, and above all make it a fun experience for you and your horse.