The Niagara Editor is one of two tools you can use to create and adjust visual effects inside Unreal Engine 4 (UE4). Before Niagara, the primary way to create and edit visual effects in UE4 was to use Cascade. While Niagara does have many of the same of particle manipulation methods that Cascade offers, the manner in which you interact and build visual effects with Niagara is vastly different.
On this page, you will find links to documentation regarding the different aspects of the Niagara Editor. If you are new to Niagara, it is recommended that you check out the Essentials section which includes a high-level overview of the Niagara Editor. In this section, you will also find an Editor Reference which breaks down components of the Niagara Editor, a Quick Start guide to quickly get you up and running, multiple How-to's which are one-off pages of how to perform certain tasks with Niagara as well as a section on Workflow tips.