I have just started learning Blender. I have a problem with the Bevel Modifier. When I use it, the model is inside the box.
How can I get rid of this box?
You have added a Bevel Modifier which is non-destructive, meaning the original geometry (8 vertices) has been preserved. Going into Edit Mode will only show the original geometry. If you want to edit this new beveled geometry, you must make that geometry final by applying the modifier. You can apply the modifier only in Object Mode with tab then clicking the ˅ button in the buttons list beside the Bevel Modifier name (which is Bevel by default) then click Apply.