You need a Tinkercad account.

Step 1: Start Making Your Cube/Sphere

First, go into Tinkercad and create an account. Then click "Create new design"

Step 2: Get the Pieces

After you have created a new project, then grab a box, sphere, and two hole boxes from the shapes slide.

Step 3: Assemble the Cube/Sphere

Take the two hole boxes and put them halfway into the solid box and sphere. You may have to extend the hole cube that is in the sphere, but that is fine. Then group the hole boxes with the solid box and the sphere. Then move the cut in half sphere in front of the cut in half box. Then you're done! You have your Cube/Sphere! Enjoy!