An animation group is a collection of objects (html elements) you want to animate. Think of groups as components on the web. You can create as many groups as you'd like and have control over each one of them.
Also see the Getting Started - Create Group page.
Give a descriptive name. You can access the group using the runtime later on:
You can either select elements by clicking elements directly on your webpage, or via the Elements panel in Chrome Devtools.
Make sure to read how Spirit references elements: