Front Shield White.stl and Back Shield White.stl need to be printed with support material.
Print the Glowing Core in either Orange or Blue.
Assembly (Using the images for reference)
Press the Glowing Core into place inside Center Black, then press the front of the portal gun on top of it.
Press the Back Shield into the Rear part of Center Black.
Position the front shield over the square holes on the front of the portal gun. Attach it in place using the two identical arms from Arms Black. Press the other ends of the arms into the corresponding holes in the back end of Center Black.
Press the remaining Arm into place on the top of the Portal Gun, using the remaining hole in the front of the gun and the hole in Back Shield.