Some extra information regarding your first question.
A database allows for the storing of almost any type of information (even files, however this is not a good practice).
PHP is a programming language meant for web development mainly and allows you to write scripts that perform certain tasks. One of these could be to connect to a database,collect the information in it and display it. Or to compare a certain password (often hashed, salted) with the one stored in the database. PHP can then be used for example to write an 'if' statement to see if the password was correct and allowing certain privileges if so.
However, if you are just building a small website for yourself and you are inexperienced (and not to forget security is not that important). It would be best to just look into PHP only and start experimenting in the beginning. Even if you would use PHP to communicate with a database it would give you no advantages over only using PHP if your code is poorly (insecure) written.
Some good links with tutorials on PHP (my favorite is the second one).
http://www.w3schools.com/php/default.asphttp://www.tizag.com/phpT/Just some additional information. PHP does not allow you to create those nice interfaces you see everywhere. For that you would need to learn some other languages like HTML and CSS,