Introduction to the Triggerscript System
What are Triggerscripts and do I need them in my FM? This may be something many T3Ed users may be wondering. Triggerscripts are the tools used to make any sort of event happen in a map. Everything to do with objectives, switches/button functionality, AIs patrolling after finishing a conversation are all examples of scripting. You could make a map without scripts, but there wouldn't be much going on. So the answer to the initial question is: You definitely do need scripts in your map.
To look at the Triggerscript browser, open the Trigger Scripts dialogue box. It is available from the View menu or by clicking on the Trigger Script Editor icon (a scroll) from the toolbar along the top edge of the main T3Ed window. This is where the magic happens.
Scripts consist of Conditions and Actions. The Conditions define what will activate the script, and the Actions define what the script does when fired. Scripts are placed on actors in a map, in the properties under Scripts > Triggerscripts. You can add as many scripts to an actor as you want.
The memory and performance impact from scripts are negligible, so use as many as you need to achieve the desired effect. Don't be afraid of making "too many" scripts. There's no such thing. Despite this, I would still advise clean script-writing practices if only to ease debugging when problems crop up down the road. Don't make the scripts more complicated than you need to do what you need them to do.
(note: I'm writing this from memory with no access to the editor. I'll edit later with more specific directions for stuff)