AnimTrails are sheets of polygons driven by particles, which are emitted from the Sockets (or bones) of a Skeletal Mesh.
(00:04) - Intro and Persona
(01:57) - Creating the Material and Particle System
(05:14) - Creating the Anim Notify
(08:33) - Testing and Tweaking
(12:41) - Changing the Color Over Life
A link to the wiki for further notes is available here -