You plant them like you would any other seed, by covering with a bit of soil. But it seems like they will germinate even right on top of soil, as i've seen volunteer plants right under the mother tree that were germinating with the seed right on surface of soil. I would still cover them. But just don't use very much soil on top. Maybe just like 1/2 an inch, so as to keep them consistently moist. They send a very long tap root, so make sure to use a deep pot, if you start them in pots.
If you plant them in the shell they can take quite a long time to germinate: 6-12 months. If you remove the nut from the shell it can sprout a lot faster and more uniformly. Trick is getting the nut out without damaging it. The shell is not very hard at all so it's really doable.
Really good news is that the seeds are viable for very long time, so even though they took very long to get to you they should still sprout fine. The trees are very large so give them lots of room to grow. Minimum spacing should be 35 feet, more would be even better.