Well, according to my experience of making a website, config.php is all about the connection on how to connect your database to your website.. MySQL, sql server etc.. bootstrap.php.. Mmm, I think this is a plugin which I found in some website.
Actually, config.php can be call, depends on your php files needed to be connect to a database.
Here's my code of config.php:
$mysql_hostname = "127.0.0.1";
$mysql_user = "root";
$mysql_password = "";
$mysql_database = "sfac_als";
$link=mysql_connect($mysql_hostname,$mysql_user,$mysql_password) or die(mysql_error());
$db=mysql_select_db($mysql_database) or die(mysql_error());
In this case, there's my example of config.php, where, you can see the name of database, which you are connecting to.