People on stream was asking how to turn on Niagara so a bamping this thread. Screenshot here is quite outdated 
I still don’t understand how exacly Niagara works and didn’t able to produce any particules
So here new screens from 4.9, currently nigara consists of 2 assets Script and Effect and Effect is particule it self and script is acript which you can use in particules
Niagara Script:
Nodes you cna use in Script:
Niagara Effect with 2 emiters i placed, there currenly 2 UIs ****** it seems which you can switch between using tabs
Again i failed to generate any visible particules, it only shows me it generate something