Only you can help you install this, or you will need to find someone you trust with a control panel login. If you are getting a “Cannot select DB” error, it’s because your connection details are wrong. We cannot see the connection details and instructions for your host, and you posting them here is a bad idea. Posting an edited config does not help either.
If you would like to contact me I can help off list (check the link in my profile and find an email address there). I will need a control panel login and access to the config.php on your server (shell, FTP or some sort of file manager.)