Here's what I'd do...
Download the zip file to the Desktop.
have full rights to that folder.
Select the zip file and extract it's full contents to a folder named after the zip file - that's the default for most zip/unzip apps.
Check the extracted files are in the same subfolders as listed in the zip itself.
There should only be a limited number of files in the base folder [.rb loader files etc]
A good zip/unzip app should keep them in the correct locations, so it should
Now 'select all' and right-click 'copy'.
Open the ../Sketchup../Plugins/ folder and right-click 'paste' to copy all of the files and files_inside_subfolders into the ../Plugins/ folder...
If not an 'admin' and/or there aren't appropriate access rights set you will be prompted for actions - 'Yes' to do the copy... and overwrite all preexisting files and merge preexisting folders and overwrite their contents as prompted.
Once all has been copied over remove the folder from your Desktop, and then file the downloaded zip file away somewhere safe for future reference if it is ever needed.
It's a good idea to have the folders within the Sketchup folder set with appropriate access rights - right-click Preferences > Security - users and admins should have 'full rights' to let them easily add/remove scripts to the Plugins, Styles, Components and Materials folders etc... Sometimes a standard install into the 'Program Files' folder gives limited rights to 'users' and that leads to this type of problem...
Regarding the Octane Render Binary being invalid...
You must enter the path [can select from the file browser] to a proper c:\...\octane.exe file that exists [slightly different on a MAC ?] - e.g. on a PC it might be
C:\Program Files\Refractive Software\OctaneRender_COM_1022_beta22_RC3_win_32\octane.exe