Hi
You need to upload the files to your server via FTP, once the files are uploaded, then visit your website, where your files where uploaded, usually is your domain, but if you uploaded the files in a folder, then it should be something like "yourdomain.com/foldername/". You will continue with the install, a process that has to be made only once. Once the installation is complete, the message will not show anymore, so people will be able to visit your website.