How to attach an armature to a model? I'm trying to get this rectangle to move based on the armature inside of it but it's not working.
Everything I've read told me to select both the armature and the model and then parent with automatic weights but nothing happens when I do that, not even an error comes up.
How do I fix this?
Are you sure you did With Automatic Weights? It really looks like you parented the armature to the cube, with the cube as the parent. That's wrong. The cube must be the child.
Make sure you select the objects in the correct order. The so-called active object is displayed orange. The so-called selected objects are displayed red.
The cube must be the child (=red), selected first in the viewport. The armature must be the parent (=orange), selected last. After you parented them With Automatic Weights (Ctrl+P in Object mode) you will see the hierarchy in the outliner. The armature is in the collection, and when you expand the node you will see the cube.

In Pose mode you can deform the mesh.