If you have a openpilot compatible car, it has a lane keeping assist camera mounted to the windshield behind the rearview mirror. The giraffe plugs between that camera and the wires that go to your car.
In order to access the plug, you will need to remove the camera cover. These are different resources depending on your car.
Other cars are probably similar.
For info on what the individual switches are, see giraffe Readme
Attach the Panda to the Giraffe OBDII port before connecting the Giraffe to the camera. Unplug the cable going to the car from the receptacle in the camera and install the giraffe between them, firmly seating the car cable into the giraffe and the giraffe into the stock ADAS camera, and plug the EON into the panda USB port.
Next see Installing EON and the software guides linked there.