If you're referring to the second one, then, I've done a tutorial for this,
Map Battle Monster Encounters (http://rmrk.net/index.php/topic,45015.0.html)
But if you just want an enemy boss character to disappear after defeat, just use control switches to swap event pages and on the next page leave no graphic for it.
Like so:
>Battle Processing: Ogre
>Control Self-Switch: A
Create a new event page and under conditions, set it to 'Control Switch A'
and leave no picture in the graphic area.