To install, just extract the contents of the zip into your Baldurs Gate 3\Data folder. This should be in your primary installation folder, not in your Appdata. Again, not in your AppData folder, this goes in the main installation location, in the Data folder. If you're struggling to find the folder, and at least if you have Steam, right click on the game in your Steam list, go down to Manage, then click Browse Local Files.