Two methods of getting in and out of the Falcon are shown in Episodes 4-6. The loading ramp underneath the right side docking arm the the top hatch above the left side docking arm. This is the hatch that Lando pulls Luke in when he rescues him at Bespin in Empire Strikes Back. I've modeled both.
Luke and R2-D2 next to the main loading ramp
Luke looking out the right side upper hatch.
Back to Ben's Millennium Falcon