The Activation Code comes inside the MERGE Cube packaging. You can find it under the Cube on a purple square. This code can only be used once, and will be tied to your user account.
The Object Viewer Code is generated when you upload a 3D object in the “My Objects” section of MERGE Miniverse (you must be logged in Miniverse to upload objects). You can share this code with other people so they can view your 3D object using MERGE Cube and the “Object Viewer” app. Here’s a list of Object Viewer codes to get you started.