Download and Install Mission Planner
This section helps you complete the Download Mission Planner step of the Hardware Setup process (using the Hardware Setup screens).
Mission Planner (MP) is a ground control station software used for configuring and managing ArduPilot-based autopilots. In this step, you will download and install Mission Planner to enable communication between your computer and either your ArduPilot hardware or a deployed host target running SITL (Software-In-The-Loop).

Click on the link from the Download Mission Planner screen and install the Mission Planner software.
Next Steps
Build the ArduPilot Firmware.