To seed in some ideas into this thread… 
The most simple way to interact with Forma is to generate any form of Geometry in Dynamo that tickles your fancy, and simply send that to Forma!
In the graph above, there are 2 Forma nodes and an optional Codeblock that dictates color 
Pretty simple!
Those nodes are GetSite (Which allows you to pull the current Site you are working on, and the SendGeometryToForma node which does exactly that… sends geometry! You can send it with no properties by using an empty dictionary, or send a color which is way more fun! The color simply uses a key of color and a color hex code, of which you can google your favorite 
But @solamour I ran that and nothing happened! 
Well fear not Dynamo-Forma explorer - you may have what I have in my site… elevation to contend with! Even a flat site may be above sea level, and in Forma, terrain is appropriately set. So have a look underneath the ground 
Hurrah - we found it our golden crown 
And that’s it! Simple enough to explore, play with and push all kinds of funky geometry into Forma 
DynamoForma_TSpline_Crown.dyn (45.6 KB)
But maybe you wanted your geometry to, you know, not be hidden underneath the ground. While the Dwarven halls in Lord of the Rings are epic, most of us live above ground. So how do we do that?
You can either put a z-value slider on your graph and play with it that way, or use the Terrain.ElevationAt node to put it correctly on the ground plane. We’ll be taking the latter path, which requires you to add a couple more nodes to your graph.
We have now added the GetTerrain node that allows us to pull the Terrain from Forma, and the Terrain.ElevationAt node that allows us to query the terrain height at those X and Y locations. We’ve also then made the executive decision to buffer up 10m more (Noting Forma works in meters today) and translate our Golden Crown upwards by those values 
Now our awesome golden crown is above the terrain! Sort of… you’ll notice that we didn’t pick the highest elevation, but rather the center of the crown, so some of it is still underground. This illustrates an interesting point to navigate should you be working on steep slopes; the need to design around them!
But what if you wanted to pick where the crown manifested? Or pick a couple of points? Say… the top of a building?
We need to add in a handful of more nodes now - it’s getting a little complex after all! 
This removes our approach in above, and adds in a new one. We add the SelectElements node, allowing us to use the Dynamo Player UI in Forma to pick something (Like a building!), followed by an Element.VolumeMesh node that allows us to get the geometries vertices and indices. We then use a swathe of Dynamo nodes to get the top vertices only, prune duplicates, generate a polygon and then pick that polygon’s center from them. After we have that point, we can generate a CoordinateSystem from it to transform our golden crown too 
We can also learn that all DynamoForma nodes are set to isInput or isOutput by default… so if something is going wrong, check you didn’t autopilot turning those off! It’s the yin to our yang’s default where they are off in Dynamo 
So we can then select a building in Forma and … voila! We have a floating flying crown-lien spaceship? 
