Simulation Events are used for setting up your scene environment before running the simulation, but they are also useful for running custom actions required for your workflow or specific shot.
A Simulation Event has a set of methods which are called during the simulation at different stages. They are called in the following order:

1. Init simulation (at the beginning of the simulation, before the first frame)

2. Init frame (at the beginning of each frame)

3. Compute frame (for every frame)

4. End frame (at the end of each frame)

5. End simulation (at the end of the simulation - after the last frame)

Simulation Events also have few other methods which are run at specific stages:

1. Load (when the event is loaded)

2. Unload (when the event is unloaded) 
3. Reset Simulation (on resetting the simulation)

Users can create new Simulation Events to customize their workflow. 
Currently, two specialized Simulation Events exist, Agent types and Animation clips.

• An Agent type is an Agent definition. It contains a skeleton definition, proxy geo and skinned geo. You can also assign a State Machine and a scale multiplier to it.
  For more information, please check out the Agent type page.
• An Animation clip defines a new clip that can be used by any of your agents. Users have to provide an Fbx, Usd or Atomsclip file and some other details such as start and end frames, loop and idle states, direction, etc.  
  For more information, please check out the Animation clip page.