This thing is meant to sit in a standard Solo plastic cup. It allows you to place an avocado pit in it and it will hold it in place better than the normal toothpicks that are used. Plus it is 3D printed and looks kind of neat.
Updated 6/13/2012: New Top Connector that snaps onto the cup; no glue necessary. Also added a fully assembled SKP.
1) Print the Full Plate or 3x Legs, 1x Top Connector and 1x Bottom Connector. I suggest printing with 2 perimeters, 0 solid layers, .125 fill density, honeycomb fill pattern, infill every 1 layers.
2) (Optional) Super-glue the parts together - be sure to keep the top and bottom connectors in the proper orientation since the slots are angled.
3) Place (optionally super-glue) the assembled thing into a Solo cup. I chose to glue it because it makes it completely sturdy.
4) Place the avocado pit in the thing pointy-side-up.
5) Fill with water to about half-way up the pit.
6) Place on a sunny windowsill and wait a few weeks. The pit should split at the top.
7) See here for more information: http://www.thehungrymouse.com/2009/09/09/how-to-grow-an-avocado-tree-from-an-avocado-pit/
8) Keep the cup so you can reuse it next time you crack open an avocado!