If you are unaware of laravel folder structure then this article may help you. Laravel framework has different folder structure. The file structure is different from your common php application. Please check attached below image to know more about laravel folder structure.
As you can see that there is not any index.php file or install folder file in the current (or root) directory. Laravel has its specific routing feature which doesn't require these files to be presented on root. You can access the installation path at http://<your_domain>/install path. Once you extract the downloaded file, you will see above files & folders in your root. Missing any one file or folder may generate errors during installation.