Controllers and limb layers
For each new limb, Limber generates three layers, which we call a set of layers: The limb layer itself, and two controllers that correspond to the position of the start (shoulder or hip) of the limb, and the end (wrist or ankle). The controllers are guide layers so that they don't appear in your final render. For simple IK animation, you’d parent the start controller to one of your character's body layers, and keyframe the end controller's Position property to animate that limb.
By default, controllers are shaped like a teardrop 💧 so that they are easy to grab in After Effects' composition panel, whilst displaying direction -the pointed end of the controller aims towards where it is rotated. You can choose a different controller shape from the settings panel if you prefer.
Two sets of Limber layers, including FK and Joint controllers
You can use buttons in the Limber panel to add two other types of controller to a limb set - FK Controllers and Joint Controllers. These types of controller should not be parented to other layers or have their Position animated by the user. Instead, they provide a layer in the timeline to which you can parent other layers, such as hands or feet, or… kneepads.