Flytekit is comprised of a handful of different logical components, each discusssed in greater detail in each link
Models Files - These are almost Protobuf generated files.
Authoring - This provides the core Flyte authoring experiences, allowing users to write tasks, workflows, and launch plans.
Control Plane - The code here allows users to interact with the control plane through Python objecs.
Execution - A small shim layer basically that handles interaction with the Flyte ecosystem at execution time.
CLIs and Clients - Command line tools users may find themselves interacting with and the control plane client the CLIs call.