How do I download the BumbleBall?
But I have absolutely no idea what to do! The instructions suck, to say the least. I downloaded the file from here like I was supposed to: Bumbleball - 'living' test element
Then I had to download something that opens up 7z files, then I followed the installation process.
*1. Put the materials, sounds and models folder to Steam\steamapps\common\portal 2\portal2*
There was no "sounds" folder inside of the BumbleBall folder. So I just put the materials and models folders there instead, wasn't sure if I was supposed to over-write the already existing models and materials folders, but I did it anyways because I had no choice.
*2. Put the Instances folder to Steam\steamapps\common\portal 2\sdk_content\maps\instances*
This one was pretty strait forward, and miraculously it worked. However, it does not show up in there in Hammer.
Now I followed (as best I could) the instructions for the "Usage"
1. Create a new func_instance
Pretty easy.
2. For the Vmf Filename' select your downloaded instance vmf's
Took about half-way into writing this for me to figure out what that meant, mostly because the Instances file I put in the other Instances file wasn't there. So I had to go to the Desktop, and open up the BumbleBall folder, go to Instances, Scottie, and then Bumbleball.vmf.
Didn't do anything.
**
3. Give it a Fix Up Name**
This is when I decided I needed help.
Also, are you sure you put it in sdk_content/maps rather than portal2[_dlcX]/maps?
AFAIK instances must be in the maps folder to work, so try it again using that one.
Also, for a "fix-up name", that's just the equivalent of a targetname. It's just a way to name your func_instance. Look in the keyvalues on the left.
Bumbleballs are fun, although so far I haven't found a test that used them. 
If the model bumbleball.mdl is in <you steam folder>/common/portal 2/portal2/models/EriksZeug/Gameplay
and the bumbleball materials in <your steam folder/common/portal 2/portal2/materials/EriksZeug/Modelle/Bumbleball/ that's good!
for the instance stuff:

Note: I chose for the dropper rather than the ball itself; but the ball should be very similar!
However, I corrected those wrong things mentioned here.