ZIP File you downloaded contains a plug-in folder. Close the Cinema 4D application and copy the content of the plug-in folder into your Cinema 4D's plug-ins folder.
Windows: c:\Users\%USERNAME%\AppData\Roaming\MAXON\CINEMA 4D (version whatever)\plugins\
Mac: Applications > Maxon > Cinema 4D (version whatever) > plugins\
Now restart the application.
Unpack the downloaded ZIP file into a temporary location of your choice (e.g. your Desktop). Inside the ZIP file you find a plug-in folder that contains all the files that need to be copied to your Cinema 4D installation.
Find Cinema 4D's plugin folder: To find the folder where Cinema 4D expects 3rd party plug-ins start Cinema 4D and go to the preferences (from the Edit > Preferences menu). You can see the path to the preferences folder at the bottom of the dialog. There is also a button to open the folder in the File Explore/Finder. Click the "Open Preferences Folder..." button.
The path for Windows is typically something like: C:\Users\Name\AppData\Roaming\MAXON\CINEMA 4D Version\
The path for Mac OS is typically something like: /Users/Name/Library/Preferences/MAXON/CINEMA 4D Version/
Close the Cinema 4D Application.
Copy the plug-in files: In the preferences folder you see a folder named plug-ins. Now copy all the files from the downloaded plugin folder into that plug-ins folder. Start Cinema 4D again. Now plug-in should be installed and working. To make sure everything went fine you can check the Console in Cinema 4D. Use the Script > Console... menu to open the Console. You should find a message showing that the plug-in has been loaded.