OpenScatter works with what is called "Scatter Systems". In the top of the addon panel you'll find a list which contains all the scatter systems in the scene.

Each scatter system can be thought of as a layer of it's own. For example, if you're working on a nature scene, you could have one layer for grass, one for some leaves, one for some clover, and so on. Each "layer" has its own settings and properties. This system makes it easy to keep everything organized and easy to work with.