Locate your installation cinema4d folder, then open folder plugins and put there plugin. Second way is put plugin into "preference" plugin folder.
Open c4d, then Edit/Preferences and at the bottom of this window is command "Open Preferences Folder...". When you click on it new window will be opened. Locate and open "plugins" folder and put plugin here.
Be sure you´ll install just in one location not both...Just single plugin...Where you put plugin it´s up to you.(Sometimes plugin developers strictly want to place their plugins into preference folder, sometimes directly into installation folder...)