Is there, plug to virustotal?
There is currently no support in core Autopsy that ties in with VirusTotal.
Here is a plugin that may do what you need https://github.com/sleuthkit/autopsy_addon_modules/tree/master/IngestModules/VirusTotal
How did I download it?
I downloaded, how to install it?
That’s what I downloaded
There is no python
You need to download the Netbeans module (nbm) file not the source code.
This is not a Python module so that section of the documentation is not relevant.