Using the default root user for all your applications is fine as long as you don’t plan on exposing any of said applications to the internet or any other people that aren’t you. Adding extra users to your MySQL server is a piece of cake and I personally like to have a different user for each application that I have.
LAMP stands Linux, Apache2, MySQL and PHP5. It is a collection of packages that create a functional web server. LAMP comes from Operating System, Web Server, Database, and Programming Language respectively. Continue reading Installing the LAMP stack