Of course, check the Documentation section of this page.

Provided you know the basics of Blender and have watched the tutorial for this pack, you shouldn't have any issues using the assets.

Yes you can, but the intended uses shown on the demo video are different in regards to the partial smoke particle effect. Because the lights are 2D, this also reduces render times and allows for fast previews. 

If you have issues in Blender 3.1 with real-time previews, then just enable playback and you will see changes instantly.

Please un-zip the archive and open the .blend project.

No, it's a plugin that uses a .blend file that has all the assets, textures and logic (node groups) inside for direct use. You can copy any of them over to any of your projects, while also preserving their original functionality. Before use, un-zip the archive.