To defeat the Celestial in level 1 of LEGO Marvel Super Heroes 2 wait for the Celestial to hit the broken down ship. Then use Star-Lord to build a sling for a gravity mine:
Go over to the sling and shoot the gravity mine at the Celestial. Jump into the ship and shoot at the green circle on the hand of the Celestial:
Go over to the hand of the Celestial and stand on the button:
Switch to Drax and climb up to the Celestial. Jump from the ship to the shoulder of the Celestial and punch the glowing box. Go into the box and turn the wheel. Switch to Star-Lord and shoot at the green ball in the Celestial:
Aim at the gravity mine and shoot the gravity mine into the Celestial:
To save the civilians behind the door in level 1 of LEGO Marvel Super Heroes 2 use Drax to turn the lever. Switch to Star-Lord and go over to the glowing light and build the cage. Jump into the cage and ride down. Use a gravity mine to clear the rubble. Switch to drax and go up to the door and mash the indicated button to break the door.