Starting Eden with this mod loaded you have two ways to go forwards:

1. To start the actual emitter editor, from the Eden menu select Tools → Emitter 3Ditor (or press CTRL + E). The tool UI will appear at the bottom of the edit area and you will get a prompt about either starting to “fiddle” with the tool or go through some of the “in-Eden” tutorials. Pressing INSERT on your keyboard will insert a single emitter to the Eden edit area on the mouse cursor position and off you can go..
2. Or, you can just place down some prop like the BMP wreck, open it’s attributes and from the attribute section Emitter 3Ditor add some particle or light effect to it.

It is highly recommended that you read this wiki through even though it’s pretty extensive, it’s not filled with just some technical jabber but shows you around the tool’s features in form of examples (with screenshots) starting with the “Attribute emitters” stuff and then moving onto the tool itself, with examples as well and only then goes deeper into the tool’s workings.
The really technical details are left towards the end of the manual.

Also before doing any serious editing with this tool you should check out the Troubles and UI Shenanigans sections.