The Modular Keyer is a schematic environment, like Batch FX, that is designed specifically keying. Within the Modular keyer, you can choose different Start Modes or presets, which generate node schematics adapted to the different keys you want to pull, such as 3D keys, chroma keys, etc.
When you start the Modular Keyer for the first time, Flame builds a default schematic that includes the 3D Keyer node, in addition to a number of other nodes, that all work well together to create and refine a basic key. This is the 3D Keyer Start Mode.

Within the Modular keyer, the keyers are represented as processing pipelines, which are collections of interconnected nodes. As you perform keying tasks in the Modular keyer, you navigate from node to node to accomplish the final key, displayed in the Result node.
As a general example, you could proceed as follows:
Because it is node-based, you have a lot of flexibility with the Modular Keyer. You can: