See the picture below for visual.

Push parts 1, 2 and 3 of the plane out of the mold so you have the individual parts.

Along the side of Part 1 push out the slot and push through part 2 the wings.

Do the same for Part 3 the tail.

To add the propeller gather the nose attachment, propeller and the bolt.

Attach the nose to the plane, pushing the bolt through the hole in the propeller into the hole of the nose.