A database is an organized storage of information. When you customize resources in your game, you sometimes want to re-use them. Say, for instance, you just imported all of XP's music tracks for use in your VX game, and you want to be able to use them in other projects you'd work on in the future. Or perhaps you've made a lot of character classes and spells that you want to transfer to future projects? You'd organize them all into a "database." This database can store everything be it music, characters, items, and even tilesets. Keep in mind, this is a simple thing to do, but when I began crafting games with the RPG Makers, I didn't think about making a database either. Here's something that will save many of you a lot of time.
First, open a new project. Name it "MY_DATABASE." This is the blank canvas for your database.
Import your BGMs, BGSs, SEs and MEs. All pictures and parallaxes you want to re-use, import them all here. Import all your graphics. Say you made a bunch of generic soldiers and wizards you want to re-use in a new tile set. Import everything you'd possibly use. Faces, animations, import everything both large and menial.
Take all your tile sets and place them in the Graphics/System folder.
Customize your classes, spells and items. Make everything. Soldiers, Wizards, Barbarians, Sages, Engineers, make everything now. Go to your spells. Customize everything and make them yours. Change the names, change the damage, change the effect, do whatever you want with them that you'll want to do again and again. Items, go change those too. Make new sets of armor and weapons, all of them your own.
Step 3b Optional
If you want different HP and attack power stats, customize everything for your Actors now. Make archetypes. Make a warrior, spell caster, cleric. Make everything now.
Grab all the scripts you'll ever need. But DO NOT PLACE THEM UNDER MATERIALS. Instead, copy all of them and place them underneath the Main process. I make an area called <Optional>. Throw everything down there. This means these scripts WILL NOT be active in the game. You do not want any active scripts right now.
Save this project. Duplicate your project whenever you start a new one. Never use "New Project" again. Instead, copy the your MY_DATABASE folder and rename it. You can even make multiple databases for tilesets. For example, I have two databases, one for the default RTP, and one for the Mack tile sets.
That should be it. Copy from this database. Every time you make a new project, you never need to import your music and graphics again. All necessary scripts are now in the database, and all tile sets should be divided in multiple folders. Enjoy.
The Unbreakable #1 Rule of Writing: Never be boring.