Why cant I copy anything I have in my Project Tab to the Hierarchy Tab or Scene?

Drag a GameObject from Project to Hierarchy, or to the scene view. Or drag a Material or Texture from Project to a mesh in the Scene view.

If that fails, turn off Play mode.

If it still fails, you'll need to give more descriptions. What exactly are you trying to copy, where exactly are you trying to copy it to, and exactly what happens when you do so.