Event Scripts are scripts written in Python 3 which utilize the Driftwood 2D scripting API to command the engine. Most of what you need to know about Event Scripts is written in the Event Scripting chapter, but a summary is given here.
After the engine starts up and loads the World Packages in its data path, the first thing it does is look for "init.py", the Init Script. This is a special Event Script which performs setup for the game. Without the presence of this script in the data path, the engine will only produce a blank window. Normally, the Init Script is a good place to set window resolution, load a first area, and insert the player entity. It must be present in the top level directory of any World Package in the path.