No ballast was provided. We used a handful of metal tokens. The furnished ammunition is a chunk of red clay intended to be rolled into balls. For goodness sake don't do that! It would get all over everywhere. We tried balls of aluminum foil (which flew tolerably well) and paper (too light to fly well). Ideally, I recommend wooden craft balls or clay marbles, if you are shooting outside. Indoors, take care to choose ammo that won't break or smudge anything.
This is the box for the kit, really a lovely presentation.

Here are the instructions and the parts. Some small parts are in a little baggie inside the bigger bag. Glue is provided. You will also need scissors and a metric ruler.

Here you can see the throwing arm, gear, and crank subassemblies. If you look closely, you can see the rubber bands holding the arm together. I'm used to just holding the pieces in place by hand until the glue starts to set, from my early days making model rockets.

These are the parts for assembling the base of the trebuchet. Drat. I seem to have forgotten to photograph that stage after assembly.

Here are the mast and the ballast bucket, with the ballast bucket lying on its side so you can see the structure.

Now the ballast bucket is sitting upright to show the inside.

Here are the new pieces lined up with the earlier ones.

The mast has been attached to the base of the trebuchet. Notice the rubber bands again for holding the pieces together.

This is a side view of the finished trebuchet. The ballast goes in the big wooden bucket, and the ammo goes in the brown felt sling. One end of the sling is fastened to the end of the throwing arm. The other has a loop that just hooks over the end so it can come loose in action. You cock this weapon by turning the crank, which raises the ballast, and the latch holds the gear in place. To fire, pull the string attached to the latched. The ballast will drop the bucket, bringing the sling end up to fling the ammo.

Here is the finished trebuchet from the front.

Recommended for history buffs, military mavens, engineers, and wooden model collectors. It's best for intermediate hobbyists, because there are a bunch of pieces and the instructions aren't ideal. Read carefully and then use your head. The result is a really handsome working model of a siege engine. I'm planning to put it next to our Lego Orthanc.