I'm absolutely new to Joomla!. I followed the instructions to install XAMPP and Joomla! 3.4.3 and everything worked. I used XAMPP's phpmyadmin to create a new database and then during Joomla! installation I just referred to the name of that database. Would it be the same if I hadn't created a database using XAMPP? I mean, if during Joomla! installation I typed an arbitrary name for a database, would it be created for me? Or is creating a database using XAMPP beforehand and then referring to this database during the installation important? I am really sorry if question is not specific enough.
In my experience, you usually don't need to create the database first on localhost environments (XAMPP, WAMP etc) when installing Joomla. Simply use
root as user, leave the password field empty (the root user password is empty by default), and type in any database name (make sure it doesn't exist already). The database will be created automatically if it doesn't exist, and the root user has all required permission for Joomla to work.
XAMPP and other similar software install with reduced security settings by default because they are not meant to be run on a live server, only in local environments for development purposes.
Obviously, when you transfer your Joomla site to a live server, you'll have to set up the database and database user before installing Joomla.
You must always create your database for before installing Joomla and then refer to it in the installation settings. This is a requirement.
Joomla will never create the database and database user for you on installation as this is a potential security risk.