You can just plant the stone in a pot and keep it watered. Pointy end up, and if the brownish skin is loose, take it off first.
The other way (suspended over a jar) works too, but the roots can be quite fragile when you come to plant it.
Unfortunately they usually die after a year or two from the cramped conditions in a pot, and lack of enough light indoors.
I have one I planted in about 1980 and have managed to keep it alive so far -- it's now about 6 ft tall, but would be a tree with fruit by now if in the ground. It was an excellent avocado, I remember.